Free Volume, Cost & Material Estimator – Updated 2026 Prices
Enter your element dimensions and concrete specification to calculate the required volume, quantities of cement, sand, and aggregate, the number of 25 kg bags required, ready-mix cost, and total project cost estimate. Covers all mix grades from GEN 0 (blinding) to C40 (structural), site-mixed and ready-mix supply.
Calculating the correct quantity of concrete for a UK construction project is one of the most fundamental tasks in building and civil engineering. Order too little and you face the expense and disruption of a second pour — with a potential cold joint weakening the structure; order too much and you pay for concrete you cannot use and face disposal costs. The calculation is straightforward for regular shapes: volume = length × width × depth for a slab, or π × radius² × height for a column. The critical step that many first-time concreters overlook is adding an adequate wastage allowance — a minimum of 10% is recommended for most applications to account for uneven formwork, spillage, and the inevitable slight over-depth in an excavated trench or slab bed.
Once the volume is established, the required mix grade must be selected. UK concrete is classified under BS 8500-1 (Concrete — Complementary British Standard to BS EN 206) using either the GEN (General) series for non-structural applications or the C (characteristic strength) series for structural concrete. The GEN series runs from GEN 0 (10 N/mm², blinding and mass fill) to GEN 4 (30 N/mm², reinforced slabs and exposed paving). The C series covers structural concrete from C20 to C50 and beyond. For most UK domestic construction in 2026, GEN 3 / C25 is the standard foundation mix and C25–C30 is the standard structural slab mix.
The choice between site-mixed and ready-mix concrete is primarily driven by volume. For volumes under approximately 0.3 m³, bagged materials (cement and all-in ballast) mixed on site with a drum mixer or by hand are the most practical option — despite being the most expensive per m³. For volumes of 0.3–2 m³, a volumetric (mini-mix) truck offers the best combination of cost and flexibility with no minimum order. For volumes above 2–3 m³ with adequate vehicle access, a ready-mix truck is almost always the most economical choice at £85–£185 per m³ depending on grade, significantly cheaper than the equivalent cost of bagged materials.
The nominal mix ratios below (by volume, using a gauge box) are the standard UK site-mix proportions for each grade. These ratios produce concrete meeting the stated strength class under normal UK conditions with properly graded aggregates:
Selecting the correct mix grade for a UK construction project in 2026 is critical — using too weak a mix risks structural failure, while over-specifying wastes money. The key considerations are the structural load, exposure conditions, and any specific durability requirements:
| Grade | Old ST Ref | Nominal Mix | Cement (kg/m³) | 28-day Strength | Ready-Mix Cost (per m³) | Typical Applications |
|---|---|---|---|---|---|---|
| GEN 0 | ST2 | 1:3:6 | 170 | ~10 N/mm² | £85–£120 | Blinding, mass fill, kerb bedding, post holes |
| GEN 1 | ST2 | 1:3:5 | 195 | ~15 N/mm² | £88–£125 | Mass fill, light strip foundations (restricted use) |
| GEN 2 | ST3 | 1:2.5:4 | 225 | ~20 N/mm² | £92–£132 | Drainage works, garage floors (light), steps |
| GEN 3 | ST4 | 1:2:4 | 270 | ~25 N/mm² | £98–£140 | Strip foundations, garden walls, domestic ground slabs – most common UK domestic mix |
| GEN 4 | ST5 | 1:1.5:3 | 320 | ~30 N/mm² | £105–£150 | Reinforced slabs, exposed paving, lightly loaded structural elements |
| C25 / RC25 | — | Designed | 340–360 | 25 N/mm² | £110–£158 | Structural foundations, ground floor slabs, columns |
| C30 / RC30 | — | Designed | 370–400 | 30 N/mm² | £120–£172 | Exposed structures, basement walls, retaining walls |
| C35 / RC35 | — | Designed | 400–440 | 35 N/mm² | £132–£188 | Heavily loaded / aggressive environments |
| C40 / RC40 | — | Designed | 450–480 | 40 N/mm² | £145–£205 | Precast, bridge decks, marine structures |
| Mix Grade | Cement (kg/m³) | Sharp Sand (kg/m³) | 20mm Gravel (kg/m³) | All-in Ballast (kg/m³) | Water (litres/m³) | Total Weight (kg/m³) |
|---|---|---|---|---|---|---|
| GEN 0 | 170 | 510 | 1,020 | 1,680 | 180 | ~1,880 |
| GEN 1 | 195 | 545 | 990 | 1,665 | 185 | ~1,915 |
| GEN 2 | 225 | 565 | 970 | 1,650 | 188 | ~1,948 |
| GEN 3 | 270 | 590 | 950 | 1,635 | 192 | ~2,002 |
| GEN 4 | 320 | 620 | 920 | 1,620 | 195 | ~2,055 |
| C25 | 350 | 770 | 1,010 | — | 189 | ~2,319 |
| C30 | 385 | 755 | 990 | — | 185 | ~2,315 |
| C35 | 420 | 735 | 970 | — | 185 | ~2,310 |
| C40 | 460 | 715 | 950 | — | 184 | ~2,309 |
| Supply Method | Cost per m³ (GEN 3, SE England) | Minimum Order | Best For | Notes |
|---|---|---|---|---|
| Bagged ballast + bagged cement | £180–£280/m³ | No minimum | Under 0.3 m³ | Most expensive per m³; widely available at DIY retailers; convenient for tiny pours |
| Bulk ballast + bagged cement | £90–£145/m³ | 0.5 tonne ballast | 0.3–2 m³ | Good value; requires site space; bulk delivery £60–£120 |
| Ready-mix (truck delivered) | £98–£140/m³ | Typically 3–6 m³ | Over 2 m³ with access | Best value above minimum; short unload window; delivery charge £150–£300 |
| Mini-mix / volumetric (delivered) | £120–£175/m³ | No minimum | 0.5–5 m³ | Mixed on site; no minimum; ideal for poor access; higher per-m³ cost than truck |
Find concrete suppliers UK 2026: CEMEX Ready Mix UK | Aggregate Industries | Hanson Concrete | The Concrete Centre | Checkatrade – Find a Concreting Contractor
| Item / Extra | Typical Cost Range (2026) | Notes |
|---|---|---|
| Ready-mix delivery charge | £150–£300 per delivery | Included for orders over plant minimum (3–6 m³); charged separately for smaller orders |
| Short-load surcharge (ready-mix) | £100–£200 per delivery | Most plants charge for orders below minimum; consider mini-mix for small volumes |
| Concrete pump hire | £350–£700/day + per m³ pumped | Line or boom pump for poor access; adds £8–£20/m³ to material cost |
| Drum mixer hire (per day) | £40–£80/day | 130–150 litre capacity; suitable for up to approx. 1 m³ per day with labour |
| Formwork / shuttering (per m²) | £8–£25/m² (materials only) | Timber boards, props, and stakes; for slab edges, walls, and columns |
| Formwork labour (design and erect) | £20–£50/m² of formed face | Carpenter / formwork operative; more complex forms cost significantly more |
| Steel reinforcement (see rebar calculator) | £580–£850/tonne supply; £200–£500/tonne fix | Required for all structural concrete; structural engineer's design essential |
| Concrete placing and finishing labour (per m²) | £12–£35/m² | Pouring, compacting, screeding, and surface finishing; floor quality finish at higher end |
| Power float / helicopter finish | £8–£18/m² | Machine-finish for smooth, hard-wearing floor surface; requires correct mix consistency |
| Polythene DPM (damp-proof membrane) | £0.50–£1.50/m² | 1200-gauge sheet under ground floor slabs; prevents ground moisture rising |
| Curing compound or cover | £0.20–£1.00/m² | Essential in warm or windy weather to prevent surface cracking; polythene sheeting adequate for most uses |
| Concrete test cubes (per set) | £80–£200 per set of 6 | Quality assurance for structural concrete; tested at 7 and 28 days at UKAS-accredited laboratory |
| Skip hire (washout and waste) | £200–£450 per skip | Ready-mix trucks must wash out on site; provide a designated washout area or arrange skip |
| Saturday / weekend delivery surcharge | £50–£150 | Premium rate for weekend and bank holiday ready-mix deliveries at most plants |
For most UK domestic projects in 2026, GEN 3 (ST4, 1:2:4 mix) is the standard and most widely used concrete grade. It meets the minimum requirements for strip and trench-fill house foundations under Building Regulations, is appropriate for garden wall footings, and provides adequate strength (approximately 25 N/mm² at 28 days) for most non-structural ground floor slab applications. It is the default recommendation when no specialist structural design is in place.
A minimum 10% wastage allowance should always be added to the calculated net concrete volume before ordering or mixing. Wastage arises from: uneven formwork allowing slight over-depth; spillage during pouring; residual concrete in mixer drum; and variation in the ground or formwork profile. For irregular shapes or uneven ground, increase the wastage allowance to 15–20%. Running short of concrete mid-pour and creating a cold joint is a far more serious and expensive problem than having a small amount left over.
The water-cement (w/c) ratio is the single most important factor controlling concrete strength and durability. A w/c ratio of 0.5 (0.5 litres of water per kg of cement) produces stronger, more durable concrete than a w/c ratio of 0.65 with the same cement content. The most common site error is adding too much water to improve workability — this weakens the concrete significantly. Add water gradually and stop when the mix is workable but firm. Never add extra water at the point of discharge from a ready-mix truck.
Normal-weight structural concrete weighs approximately 2,300–2,400 kg/m³ (typically taken as 2,350 kg/m³ for calculation purposes). This is important when: calculating vehicle access load limits before ordering a ready-mix truck; checking the structural capacity of an existing floor before pouring a new topping; estimating skip weights; and understanding the loads transferred to foundations. A single ready-mix truck carrying 6 m³ of concrete carries approximately 14 tonnes of concrete alone, plus the vehicle's own weight of 10–15 tonnes.
Concrete strength gain is highly temperature-dependent. At 20°C, GEN 3 concrete achieves approximately 70% of its 28-day strength by 7 days. At 10°C, this takes approximately 14 days. Below 5°C, strength gain is very slow; below 2°C, concrete can freeze and is permanently damaged. In cold weather, insulate fresh concrete with blankets, use warm mixing water (30–40°C), and never pour concrete when the ground or air temperature is below 2°C without heating measures in place.
Ready-mix concrete must be discharged and placed within 2 hours of the water being added at the batching plant (or 300 drum revolutions, whichever is sooner) under BS EN 206. In hot weather or where plasticiser retarder has not been added, this window may be shorter. Always have adequate labour, equipment (wheelbarrows, pumps), and formwork ready before the truck arrives — concrete cannot be held in the drum indefinitely, and any delay risks the mix becoming unworkable. A typical 6 m³ pour should be planned to discharge in 30–45 minutes maximum.
When site-mixing concrete, always measure proportions by volume using a gauge box — never by shovel count, which varies enormously between operatives. A standard gauge box holds the equivalent of one cement bag (approximately 25 litres or 0.025 m³). For a GEN 3 (1:2:4) mix, use one gauge box of cement, two gauge boxes of sharp sand, and four gauge boxes of 20mm aggregate per batch. Measure all dry ingredients first, combine in the mixer or on a mixing board, then add water gradually to achieve the correct workability.
A cold joint forms when fresh concrete is placed against concrete that has already begun to set — typically when a pour is interrupted and the first load has stiffened before the second arrives. Cold joints represent a plane of weakness in the concrete and can allow water ingress. They are most commonly caused by: ordering insufficient volume; ready-mix delays; and inadequate labour to pour the full volume in one continuous operation. Always plan pours carefully to ensure the entire volume can be placed without interruption.
Concrete supply is subject to 20% standard rate VAT in most UK construction contexts. However, concrete supplied to a new residential dwelling under construction is zero-rated for VAT under HMRC's new build relief — significantly reducing the material cost. Concrete for extensions, renovations, and repairs is always standard-rated. Always clarify the applicable VAT rate with your contractor or ready-mix supplier before finalising your budget, particularly on larger projects where the VAT difference is material.
Admixtures are chemicals added to concrete to modify its properties. The most commonly used in UK domestic and commercial construction in 2026 are: plasticisers / superplasticisers (improve workability without adding water); retarders (slow setting for hot weather or long hauls); accelerators (speed strength gain in cold weather); air-entraining agents (improve freeze-thaw resistance in exposed paving); and waterproofing agents (reduce permeability). Most admixtures are added at the batching plant for ready-mix concrete; for site-mixed concrete, follow the manufacturer's dosage instructions precisely.
Fresh concrete must be properly compacted to eliminate air voids and ensure full contact with formwork and reinforcement. For most applications, compaction is achieved by internal vibration (using a poker vibrator) or by tamping (striking repeatedly with a beam across the surface). Insufficient compaction produces honeycombed concrete with reduced strength and durability. Poker vibrators should be inserted vertically at approximately 500mm centres and withdrawn slowly — leaving for too long causes aggregate segregation. For very stiff (low-slump) mixes, compaction is critical; for fluid self-compacting mixes, vibration is not required.
Concrete's embodied carbon is dominated by the Portland cement (CEM I) content, which carries approximately 0.83–0.90 kg CO₂e per kg. For a typical GEN 3 mix (270 kg cement/m³), the embodied carbon is approximately 225 kg CO₂e/m³. For a C30 mix (385 kg/m³), approximately 320 kg CO₂e/m³. The most effective way to reduce concrete embodied carbon is to replace Portland cement with GGBS or PFA — at 50% GGBS replacement, embodied carbon falls by approximately 40%. Reducing over-specification (using GEN 3 where GEN 3 genuinely suffices rather than automatically specifying C30) also saves significant carbon.
| Application | Recommended Mix | Min. Thickness | Reinforcement | Key Considerations |
|---|---|---|---|---|
| Blinding layer (over formation) | GEN 0 | 50–75mm | None | Non-structural; provides clean working surface; no strength requirement |
| Garden wall footing | GEN 3 | 150–200mm deep; 450–600mm wide | None (unreinforced) | Must be below frost line (450mm to base); 3× wall thickness wide |
| House strip foundation | GEN 3 / C25 | 225mm min. (BC) | None unless designed | Building Regulations require min. GEN 3; structural engineer for non-standard sites |
| Trench fill foundation | GEN 3 / C25 | Fill trench to 150mm below surface | None typically | Self-levelling; fluid consistency preferred; use 40mm aggregate |
| Domestic ground floor slab | GEN 3 / C25 | 100mm min. | A142 or A193 fabric or T12@200 | Over compacted hardcore and DPM; power float for smooth finish |
| Garage floor slab | C25–C30 | 150mm | A252 fabric or T12@150 | Vehicle loading; thicker and stronger than domestic slab; power float |
| Driveway concrete | C30 + air entrained | 150mm | A252 or T12@150 recommended | Air entrainment (3–5%) for freeze-thaw resistance; broom finish for grip |
| Concrete steps (garden) | GEN 3 / C25 | 100mm riser; 150mm base | T8–T10 for risers | Stiff mix to retain shape; brush finish for grip; exposed aggregate option |
| Reinforced beam | C25–C30 | Designed | Structural design required | Eurocode 2 design; cover to reinforcement critical; vibration essential |
| Reinforced column | C30–C35 | Designed | Structural design required | High binder content; use 10mm aggregate for congested reinforcement |
| Basement retaining wall | C30 + 50% GGBS | 250mm min. | Structural design required | Low permeability critical; GGBS reduces heat and improves durability |
| Mass raft foundation | C25–C30 + 60–70% GGBS | Designed | Structural design required | High GGBS reduces heat of hydration and thermal cracking risk |
For a rectangular slab or foundation, the formula is simple: length (m) × width (m) × depth (m) = volume in m³. For a circular column: π × radius² × height. For a wall: length × height × thickness. Always add a minimum 10% wastage allowance to the calculated volume before ordering — so multiply your net volume by 1.10. For a typical domestic project (e.g. a 4m × 3m × 0.15m slab): 4 × 3 × 0.15 = 1.80 m³ net; with 10% wastage = 1.98 m³ — round up to 2.0 m³ to order. Use this calculator to handle all common shapes automatically with the correct wastage.
For a shed base with light foot traffic only, a minimum of GEN 3 (1:2:4 mix) at 100mm thickness is appropriate. For a garage floor subject to vehicle loading (car, van, or light truck), specify a minimum of C25 at 150mm thickness, with A252 fabric reinforcement or T12 bars at 150mm centres. For a garage used regularly by heavy vehicles or for a workshop floor subject to point loads, upgrade to C30 at 150mm with reinforcement and consider a power-floated finish for durability. Never use GEN 0 or GEN 1 for floors — they are too weak and will dust and crack under traffic.
Ready-mix concrete costs approximately £85–£120/m³ for GEN 0 up to £145–£205/m³ for C40 in South East England in 2026, plus a delivery charge of £150–£300. The most common domestic grade — GEN 3 / C25 — costs approximately £98–£155/m³ for ready-mix. Site-mixed from bulk aggregate costs approximately £90–£145/m³ in materials. Bagged materials from a DIY retailer cost approximately £180–£280/m³ — the most expensive option but practical for volumes under 0.3 m³. For volumes of 0.5–2 m³ without good truck access, a mini-mix (volumetric) truck at approximately £120–£175/m³ is usually the best value. Always obtain current quotes — concrete prices fluctuate with cement and energy costs.
Both C25 and GEN 3 are approximately 25 N/mm² characteristic compressive strength at 28 days, but they are specified under different systems. GEN 3 is a prescribed (nominal) mix under BS 8500 — the mix proportions (1:2:4 by volume) are specified rather than the strength, so actual strength depends on the quality of the constituent materials and workmanship. C25 is a designed mix — the concrete producer is responsible for designing the mix to achieve the specified characteristic strength under BS EN 206 testing, with full quality control and compliance documentation. For domestic projects with no Building Control involvement, GEN 3 site-mixed is usually acceptable. For projects under Building Regulations or structural design, C25 designed mix from a QSRMC or BSI-certified plant is the correct specification.
For a GEN 3 (1:2:4) mix, you need approximately 270 kg of cement per m³ of finished concrete — approximately 11 × 25 kg bags per m³. For a typical 4m × 3m × 0.15m slab (1.98 m³ including 10% wastage), you would need approximately 22 bags of cement, plus approximately 1,170 kg (47 bags) of sharp sand and 1,880 kg (76 bags) of 20mm gravel. Using all-in ballast instead: approximately 24 bags of cement and approximately 3,240 kg (130 bags) of ballast. At these quantities, bulk aggregate delivery and site mixing with a hired drum mixer is significantly more economical than bagged materials — use this calculator to find the exact quantities and choose the most cost-effective supply method.
Yes — hand mixing is feasible for very small volumes (up to approximately 0.05–0.1 m³, equivalent to a couple of large buckets of finished concrete). Lay a mixing board or use a large trough. Combine the dry ingredients thoroughly until uniform in colour, then make a well and add water gradually, working from the outside inwards. Hand mixing is laborious, slow, and difficult to achieve consistent results with — for anything more than a few litres of concrete, a hired drum mixer (£40–£80/day) is strongly recommended. It reduces labour significantly, produces a more consistent mix, and is available from most hire shops. Never attempt to hand mix more than a few bags' worth of concrete for any structural purpose.
Concrete sets (becomes rigid and can no longer be worked) within approximately 2–4 hours of mixing at 15–20°C. However, setting is not the same as curing — concrete continues to gain strength for weeks. Practical milestones for GEN 3 / C25 concrete at 15–20°C are: walk on carefully after 24 hours; formwork can be removed from edges after 24–48 hours; light vehicle access after 7 days; full vehicle loading after 28 days. In cold weather (below 10°C), extend all these timescales significantly. In hot or windy weather, begin curing (cover with damp hessian or polythene) as soon as the surface has lost its sheen to prevent premature drying and surface cracking.
Ready-mix concrete is concrete produced at a centralised batching plant and delivered to site in a rotating drum truck, ready to pour. It is the most economical supply method for volumes above approximately 2–3 m³ with adequate vehicle access to the pour point. Advantages over site mixing include: guaranteed mix consistency and quality; no need for on-site plant or aggregate storage space; faster pouring (a 6 m³ truck can be discharged in 20–30 minutes with adequate labour); and full compliance documentation for structural applications. The main constraints are: minimum order quantities (typically 3–6 m³, with short-load surcharges below this); the need for good vehicle access (an 8-wheel truck with 6 m³ of concrete weighs approximately 25 tonnes); and the requirement to have adequate labour and formwork ready before the truck arrives — concrete cannot be stored once discharged.
Whether Building Regulations approval is required for a concrete slab depends on the use and context. A simple garden shed base or patio slab does not require Building Regulations approval. A garage floor forming part of a garage that is attached to the house or forms part of the habitable envelope may require approval depending on the extent of the works. Any concrete work forming part of a house extension, new build, or structural alteration will require Building Regulations approval, and the concrete specification must be confirmed with your Building Control officer — typically GEN 3 minimum for foundations, with structural engineer's design for anything non-standard. If in doubt, contact your local authority Building Control before commencing work.
The most effective ways to reduce concrete embodied carbon in UK projects in 2026 are: specify GGBS or PFA cement replacement — at 50% GGBS, binder carbon falls by approximately 43%; at 70% GGBS, by approximately 60%; avoid over-specification — use GEN 3 where GEN 3 genuinely meets requirements rather than automatically specifying C30; minimise concrete volume through efficient structural design (thinner slabs with appropriate reinforcement rather than thick unreinforced slabs); and specify concrete from plants with Environmental Product Declarations (EPDs) showing actual carbon content, enabling informed comparison between suppliers. The RIBA 2030 Climate Challenge targets a 40–50% reduction in structural embodied carbon by 2030 — concrete specification is the primary lever in achieving this for most projects.
For concrete work in the UK, seek recommendations from neighbours or other tradespeople; check reviews on Checkatrade, TrustATrader, or Google; and obtain a minimum of three written quotations. Confirm that the contractor: carries public liability insurance (minimum £1 million); is experienced with the specific type of work you require (foundation pouring is different from floor finishing); can confirm the ready-mix plant and mix specification they plan to use; and can provide references from recent comparable projects. For structural concrete under Building Regulations, ensure the contractor understands the specification requirements and will provide the necessary compliance documentation. Never accept a concrete quotation that simply says "concrete slab" without specifying the mix grade, thickness, reinforcement, finish, and what is and is not included in the price.
Additional concrete resources UK 2026: The Concrete Centre | CEMEX UK – Ready Mix | Aggregate Industries | BSI – BS 8500 / BS EN 206 | GOV.UK Building Regulations | Checkatrade – Find a Concreting Contractor