Free GEN 3 Concrete Volume & Cost Estimator – Updated 2026 Prices
Enter your project dimensions below to calculate the volume of GEN 3 concrete required and estimate the cost of ready-mix supply in the UK in 2026. GEN 3 concrete (equivalent to C20 / ST4) is widely used for domestic foundations, garage slabs, paths, and general groundworks.
GEN3 concrete (also written GEN 3) is one of the standardised concrete mix designations defined in the UK standard BS 8500-2:2015+A2:2019, which replaced the old ST (Standard) and C (Characteristic) mix designations for ordinary structural concrete. GEN3 is equivalent to the older ST4 designation and is broadly comparable to C20/25 in European notation — meaning it achieves a characteristic compressive strength of approximately 20–25 N/mm² at 28 days. It is the workhorse concrete of UK domestic construction in 2026, specified for a huge range of general groundworks and foundation applications where higher structural performance (such as that required by C30 or C35) is not needed.
In 2026, the cost of GEN3 ready-mix concrete in the UK ranges from approximately £90–£115 per m³ in North England, Wales, Scotland, and Northern Ireland up to £120–£155 per m³ in South East England and Greater London for standard drum-mixer delivery in full-load quantities (typically 6–8 m³). Short loads (under the minimum load threshold, typically 4–6 m³ depending on the plant) attract a short-load surcharge of £80–£200 per m³ below the minimum, which can significantly increase the effective cost per m³ for small pours. Volumetric mixer trucks (which mix concrete on-site to the exact quantity required) eliminate the short-load penalty and are often more cost-effective for pours between 0.5 m³ and 4 m³, typically priced at £130–£180/m³ including the volumetric mixing premium.
GEN3 concrete is specified for a wide range of domestic construction applications where a general-purpose, moderate-strength concrete is required but where the higher performance of GEN4 (C25) or RC30/RC35 is not necessary. Typical UK applications in 2026 include: strip and trench-fill foundations for single-storey extensions, garages, and outbuildings; oversite concrete (the plain slab below a timber or beam-and-block suspended floor); domestic paths, patios, and driveways; post and pad bases for garden structures, pergolas, and gate posts; trench backfill where an engineered lean mix is required; and general small pours where concrete strength is not the primary design criterion.
A GEN3 concrete mix in the UK in 2026 typically contains the following constituents by weight (approximate proportions for a 1 m³ batch):
The equivalent site-mix proportions for a GEN3 / C20 concrete are approximately 1 part cement : 2 parts sand : 4 parts coarse aggregate by volume (1:2:4 mix), or alternatively 1 part cement : 3 parts all-in ballast (1:3 ballast mix). However, site-mixing is inherently less consistent than ready-mix and should only be used for very small pours (under 0.25 m³) where ready-mix or volumetric delivery is impractical. The quality and consistency of ready-mix concrete from a BS EN 206-compliant batching plant is significantly superior to site-mixed concrete, and the cost difference is often smaller than expected once the labour and equipment costs of site-mixing are accounted for.
The BS 8500 GEN series (GEN1 through GEN4) covers standardised mixes for general, non-structural, and lightly structural domestic applications. Understanding where GEN3 sits in this hierarchy helps specify the correct concrete for any given application:
GEN3 concrete resources UK 2026: The Concrete Society | BSI – BS 8500 Standard | Quarry Products Association | Checkatrade – Find a Groundworks Contractor
The table below provides a comprehensive price guide for GEN3 concrete supply in the UK in 2026, broken down by supply method and region. All prices are per cubic metre (m³) indicative mid-range estimates for standard 20mm aggregate, S3 slump, excluding short-load surcharges. VAT is not included.
| Supply Method | N Ireland / Scotland | North England / Wales | Midlands / SW | South East | Greater London |
|---|---|---|---|---|---|
| Ready-Mix – full load (6+ m³) | £90–£105/m³ | £95–£112/m³ | £100–£120/m³ | £108–£132/m³ | £120–£148/m³ |
| Ready-Mix – short load (2–5 m³) | £110–£135/m³ | £118–£145/m³ | £125–£155/m³ | £135–£168/m³ | £150–£190/m³ |
| Volumetric Mixer (any quantity) | £120–£145/m³ | £128–£158/m³ | £135–£168/m³ | £145–£180/m³ | £160–£200/m³ |
| Site-Mixed (cement + ballast) | £135–£175/m³ | £140–£185/m³ | £145–£190/m³ | £155–£200/m³ | £165–£215/m³ |
| Bagged GEN3 Mix (25kg bags) | £185–£240/m³ | £190–£250/m³ | £195–£260/m³ | £200–£270/m³ | £210–£285/m³ |
| Concrete pump hire (additional) | £300–£550/day | £350–£600/day | £375–£650/day | £400–£700/day | £450–£800/day |
Prices are indicative mid-range 2026 supply estimates, excl. VAT. Ready-mix prices vary significantly between plants and regions — always obtain at least three quotes from local batching plants. Concrete prices are affected by cement commodity costs (linked to energy prices) and aggregate availability, and can change year-on-year by 5–15%.
| Application | Typical Depth | Coverage at that Depth | Typical Pour Size | Volume Required | Indicative Supply Cost (SE) |
|---|---|---|---|---|---|
| Oversite / blinding | 75mm | 13.3 m² per m³ | 25 m² (single garage) | 1.9 m³ | £250–£350 |
| Path / patio slab | 100mm | 10.0 m² per m³ | 20 m² | 2.0 m³ | £270–£390 |
| Domestic driveway | 125mm | 8.0 m² per m³ | 30 m² | 3.75 m³ | £490–£720 |
| Garage slab (single) | 150mm | 6.7 m² per m³ | 25 m² | 3.75 m³ | £490–£720 |
| Garage slab (double) | 150mm | 6.7 m² per m³ | 42 m² | 6.3 m³ | £820–£1,200 |
| Strip foundation (single) | 200mm | 5.0 m² per m³ | 20 m run, 450mm wide | 1.8 m³ | £240–£360 |
| Trench fill foundation | 450mm | 2.2 m² per m³ | 20 m run, 600mm wide | 5.4 m³ | £700–£1,050 |
| Post / pad base | 300mm | — | 600×600mm pad × 6 no. | 0.65 m³ | £120–£180 (volumetric) |
All volumes include a 10% wastage allowance. Indicative supply costs are for South East England, excl. VAT. Short-load surcharges apply to orders below the batching plant minimum (typically 4–6 m³). Consider volumetric mixer supply for pours under 4 m³ to avoid short-load penalties.
The following additional costs are commonly associated with GEN3 concrete projects in the UK in 2026 and are typically not included in the basic concrete supply price.
| Item / Service | Typical Cost Range (2026) | Notes |
|---|---|---|
| Short-load surcharge | £80–£200 per m³ below minimum | Applies when ordering below the plant minimum (typically 4–6 m³); order volumetric instead for small pours |
| Concrete pump hire (line pump) | £400–£800 per day | Required for restricted-access sites; typically includes operator; minimum half-day charge |
| Concrete pump hire (boom pump) | £700–£1,500 per day | For large pours or long reach; minimum 4–6 m³ pumped to be economical |
| Plasticiser admixture | £3–£8/m³ surcharge | Improves workability without adding water; useful for reinforced pours and confined spaces |
| Accelerator admixture | £5–£12/m³ surcharge | Speeds up set – useful in cold weather or where early strength gain is needed |
| Retarder admixture | £4–£10/m³ surcharge | Slows set – useful in hot weather or for large continuous pours |
| Air entrainment admixture | £4–£10/m³ surcharge | Creates micro air bubbles for freeze-thaw resistance – recommended for exposed paths and driveways |
| 10mm aggregate (instead of 20mm) | £3–£8/m³ surcharge | Finer aggregate for thinner sections, heavily reinforced areas, or pumped concrete |
| Fibres (polypropylene or steel) | £5–£15/m³ surcharge | Added to mix to reduce plastic shrinkage cracking; does not replace structural reinforcement |
| Concrete delivery wait time | £2–£5 per minute after free time | Most plants allow 5–10 minutes per m³ unloading time; ensure formwork and labour are fully ready |
| Saturday / out-of-hours delivery | £80–£200 surcharge per load | Weekend and bank holiday deliveries attract a premium — plan to pour Monday–Friday where possible |
| Concrete test cube service | £80–£200 per set of cubes | 6 cubes taken from pour, cured, and crushed at 7 and 28 days to confirm strength — often required by Building Control |
| Tamping / levelling labour | £8–£18/m² | Labour cost to spread, tamp, and level concrete after pour; power float finish additional |
| Power float finish | £4–£9/m² | Creates smooth, dense, dust-resistant surface on slabs; typically done 2–4 hours after pour |
| Curing compound (spray-on) | £0.80–£2.50/m² | Sprayed on freshly finished slab to reduce moisture evaporation and surface cracking |
| Formwork / shuttering (timber) | £3–£8/m² of slab perimeter | Edge shuttering to contain pour; typically 150×25mm timber planks; can be removed after 24–48 hours |
GEN3 concrete is the same mix as the older ST4 (Standard Mix 4) designation and is broadly equivalent to C20/25 (European notation), with a characteristic compressive strength of approximately 20–25 N/mm² at 28 days. All three designations are still used interchangeably in the UK trade in 2026, though BS 8500 GEN terminology is the current standard.
Most UK ready-mix batching plants have a minimum order of 4–6 m³ for drum-mixer delivery. Orders below this minimum are either refused or subject to a significant short-load surcharge (£80–£200 per m³ below the minimum). For pours under 4 m³, a volumetric mixer (which mixes on-site to the exact quantity) is usually more cost-effective.
Ready-mix concrete is always preferred over site-mixed concrete for pours over 0.25 m³. Ready-mix is batched to a consistent specification, delivers better strength and workability, and — once the delivery cost is accounted for — is often cheaper than site-mixing when labour and equipment are included. Site-mixing should be reserved for very small, remote, or access-restricted pours only.
Concrete workability is measured by the slump test. For most domestic applications, an S3 slump class (100–150mm) is specified — providing good workability for placing and compacting around reinforcement. For pumped concrete, S4 (150–200mm) is typical. Always specify the minimum slump needed — adding water on site to increase workability reduces strength and increases the risk of cracking.
GEN3 concrete sets (hardens sufficiently to walk on) within approximately 4–8 hours in normal UK temperatures. It reaches approximately 70% of design strength at 7 days and 99% at 28 days. Do not apply significant loads (vehicles) until at least 7 days after pouring, and 28 days for heavy loads. Cold weather (below 5°C) significantly slows curing — protect freshly poured concrete with insulating blankets in autumn and winter.
Volume (m³) = Length (m) × Width (m) × Depth (m). Always add a 10% wastage allowance to account for slight variations in excavation depth, formwork imperfections, and spillage. Running short on a pour risks a cold joint — a structural weakness where fresh concrete is poured against partially set concrete. It is always better to over-order slightly than to run short.
GEN3 concrete is typically supplied with 20mm maximum aggregate size, suitable for most domestic pours. 10mm aggregate is specified for sections less than 100mm thick, heavily reinforced sections where aggregate needs to pass between bars, or pumped concrete (smaller aggregate pumps more easily). 10mm aggregate costs £3–£8/m³ more than 20mm.
GEN3 is not suitable for: reinforced concrete structural elements (use RC30 or RC35 minimum); exposed surfaces subject to freeze-thaw cycles without air entrainment; chemically aggressive ground conditions (use designated mix with sulphate resistance); below-ground concrete in sulphate-bearing soils; or any application where structural integrity requires a higher characteristic strength specification.
Do not pour concrete when the air temperature is below 3°C or forecast to fall below 3°C within 24 hours. Frost prevents proper hydration and permanently weakens the concrete. If pouring in cold conditions is unavoidable: use accelerator admixture; order a warmer mix (some plants can supply heated concrete in winter); and cover immediately with insulating blankets or polythene and straw.
In hot weather (above 25°C), concrete sets faster and is at higher risk of plastic shrinkage cracking on the surface. Mitigations include: ordering with a retarder admixture; pouring in early morning or evening; damping down sub-base and formwork before pour; and covering the finished surface with damp hessian or polythene sheeting immediately after finishing. Hot weather concrete planning is increasingly relevant in UK summers.
Every ready-mix delivery must be accompanied by a delivery ticket specifying the mix designation, aggregate size, slump class, w/c ratio, cement type, admixtures, volume, time of batching, and time of discharge. Always retain delivery tickets — they are the proof of concrete specification and are required by Building Control for inspections. Reject any delivery that does not come with a compliant delivery ticket.
Concrete production is responsible for approximately 6–8% of global CO² emissions, primarily from cement manufacture. Low-carbon alternatives are increasingly available from UK ready-mix plants in 2026, including mixes using GGBS (ground granulated blast-furnace slag) or fly ash (PFA) as partial cement replacements, reducing embodied carbon by 30–60% at little or no cost premium. Ask your ready-mix supplier about low-carbon GEN3 options.
The table below shows the approximate quantities of materials needed to site-mix GEN3 / C20 equivalent concrete at a 1:2:4 (cement:sand:coarse aggregate) mix ratio by volume. Site-mixing is only recommended for very small pours (under 0.25 m³) where ready-mix or volumetric delivery is not practical. All quantities include 10% wastage. Bagged cement is typically supplied in 25kg bags.
| Volume Required (m³) | Cement (25kg bags) | Sharp Sand (kg) | 20mm Aggregate (kg) | Water (litres) | Approx. Site-Mix Cost (materials) |
|---|---|---|---|---|---|
| 0.10 m³ | 2 bags (50kg) | 100 kg | 200 kg | 33 litres | £18–£28 |
| 0.25 m³ | 4 bags (100kg) | 250 kg | 500 kg | 82 litres | £42–£65 |
| 0.50 m³ | 8 bags (200kg) | 500 kg | 1,000 kg | 165 litres | £85–£130 |
| 1.00 m³ | 15 bags (375kg) | 1,000 kg | 2,000 kg | 330 litres | £165–£250 |
| 2.00 m³ | 30 bags (750kg) | 2,000 kg | 4,000 kg | 660 litres | £330–£500 |
| 4.00 m³ | 60 bags (1,500kg) | 4,000 kg | 8,000 kg | 1,320 litres | £660–£1,000 |
Site-mix material costs above are for materials only — they do not include labour (significant for large volumes), mixer hire (typically £80–£200/day for a site mixer), or delivery of bulk aggregates. For any volume over 0.5 m³, a volumetric ready-mix truck is almost always more economical when total cost (materials + labour + mixer hire) is compared. Bagged GEN3 ready-to-use mixes (available from builders’ merchants in 20kg or 25kg bags) are a convenient alternative for very small pours but cost approximately 2–3× more per m³ than volumetric or ready-mix supply.
GEN3 concrete is a standardised concrete mix designation defined in UK standard BS 8500-2, equivalent to the older ST4 and broadly comparable to C20/25 (20–25 N/mm² characteristic compressive strength at 28 days). In 2026, GEN3 is the most widely specified general-purpose domestic concrete in the UK, used for strip and trench-fill foundations for single-storey extensions, garages, and outbuildings; oversite concrete (the plain slab beneath suspended floors); domestic paths, patios, and driveways; post and pad bases for garden structures; trench backfill where an engineered lean mix is required; and any general construction application where a moderate-strength, general-purpose concrete is needed but full structural RC30/RC35 performance is not required.
In 2026, GEN3 ready-mix concrete costs approximately £90–£105/m³ in Northern Ireland and Scotland, £95–£112/m³ in North England and Wales, £100–£120/m³ in the Midlands and South West, £108–£132/m³ in South East England, and £120–£148/m³ in Greater London for full-load drum-mixer delivery (6+ m³). Short loads (under 4–6 m³) attract surcharges that can increase the effective per-m³ cost by 30–80%. Volumetric mixer supply (no short-load penalty) typically costs £130–£180/m³ depending on region. Always obtain at least three quotes from local batching plants as prices vary significantly between suppliers.
The basic formula is: Volume (m³) = Length (m) × Width (m) × Depth (m). Always add a 10% wastage allowance (15–20% for strip foundations or irregular excavations). For example, a garage slab 5m × 5m at 150mm thick: 5 × 5 × 0.15 = 3.75 m³ net, plus 10% = 4.1 m³ to order. For circular pours (post bases, round pads), the formula is: π × (radius)² × depth. For strip foundations, calculate the total run of strips × trench width × concrete depth. Round up to the nearest 0.25 m³ when ordering from a batching plant. It is always better to over-order slightly than to run short — a cold joint (where fresh concrete is poured against partially set concrete) is a serious structural defect.
These three designations all refer to essentially the same concrete mix, just using different naming conventions. GEN3 is the current BS 8500-2 designation introduced to standardise concrete specifications across the UK. ST4 (Standard Mix 4) was the predecessor designation under the old BS 5328 standard, now withdrawn but still commonly used in the UK trade in 2026 — if a contractor specifies ST4, they mean GEN3. C20 (or C20/25 in European notation) is the equivalent strength class designation, referring to a concrete with a characteristic cylinder strength of 20 N/mm² (cube strength approximately 25 N/mm²). All ready-mix plants in the UK will understand any of these designations and supply the same mix — but always quote the BS 8500 GEN3 designation on any specification or order to avoid ambiguity.
GEN3 (C20) is not recommended for reinforced concrete applications in current UK practice. When steel mesh (A142 or A193) or rebar is incorporated into a slab or foundation, the minimum concrete grade should be RC30 (C30) in accordance with BS 8500 and the requirements of Eurocode 2 (BS EN 1992). Using GEN3 with reinforcement risks inadequate bond between the steel and concrete, insufficient durability of the concrete cover protecting the steel from corrosion, and failure to meet Building Regulations requirements for structural concrete elements. For a standard domestic garage slab with A142 mesh reinforcement, always specify RC30, not GEN3 or C20. GEN3 is appropriate for unreinforced oversite concrete, plain strip foundations, paths, and pad bases without structural rebar.
A short-load surcharge is an additional charge applied by ready-mix batching plants when you order less than their minimum load — typically 4–6 m³ depending on the plant and region. The surcharge compensates the plant for the inefficiency of running a partially loaded drum mixer truck, and is typically £80–£200 per m³ below the minimum. For example, if the minimum load is 6 m³ and you order 3 m³, you may pay a surcharge of 3 × £120 = £360 on top of the basic concrete cost. To avoid short-load surcharges: use a volumetric mixer (which mixes on-site to the exact quantity, typically £130–£180/m³ including the volumetric premium); combine your pour with a neighbour or adjacent project; or use bagged ready-to-mix GEN3 for very small volumes (under 0.5 m³).
Slump class describes the workability (flowability) of fresh concrete and is specified as follows under BS EN 206: S1 (10–40mm slump): very stiff mix, used for heavily compacted road base or dry-cast products — not appropriate for domestic pours. S2 (50–90mm): stiff mix, suitable for foundations and slabs where no pumping is required and good compaction is achievable. S3 (100–150mm): medium workability, the most common specification for domestic concrete — suitable for most unreinforced and lightly reinforced pours. S4 (160–210mm): high workability, required for pumped concrete and heavily reinforced sections. For a standard GEN3 domestic pour, specify S3 slump class as the default. Never add water on site to increase slump — this reduces concrete strength and increases shrinkage cracking.
GEN3 concrete goes through two distinct phases: setting (initial hardening, during which the concrete transitions from a fluid to a solid) and curing (the ongoing chemical hydration process that develops strength over weeks). In typical UK summer conditions: the concrete will have set sufficiently to walk on within 4–8 hours of pouring; formwork can usually be struck after 24–48 hours; light foot traffic and loading is acceptable after 3–7 days; vehicle loading should wait until at least 7 days and ideally 14–28 days; and full design strength (28-day strength) is achieved at approximately 28 days. Cold weather significantly slows curing — at 5°C, curing rate is approximately half that at 20°C. Protect concrete with insulating blankets if frost is forecast within 48 hours of pouring.
Yes — GEN3 concrete can be site-mixed for very small volumes (under 0.25 m³) using a cement mixer and bagged materials. The approximate mix ratio is 1 part cement : 2 parts sharp sand : 4 parts 20mm aggregate by volume (or 1 part cement : 3 parts all-in ballast). Each 25kg bag of cement yields approximately 0.025 m³ of concrete when mixed at 1:2:4 ratio. However, site-mixing is significantly more laborious than using ready-mix, produces concrete of variable and generally lower quality (due to inconsistent mixing, water addition, and aggregate proportioning), and is rarely cheaper than volumetric ready-mix once labour costs are accounted for. For any pour over 0.5 m³, ready-mix or volumetric concrete is strongly recommended.
A concrete pump is needed when the ready-mix truck cannot discharge directly into the formwork due to restricted access, distance, or height. Typical situations requiring a pump include: narrow side access where the mixer cannot get within 3–4m of the pour point; rear-garden pours without vehicular access; elevated pours (upper floor slabs); and large pours where moving the concrete by barrow would take too long (risking the first concrete placed beginning to set before the pour is complete). Line pumps (trailer-mounted piston pumps with flexible hose) cost approximately £400–£800/day and can pump GEN3 concrete up to 50–100m horizontally. Boom pumps (truck-mounted with articulated arm) cost £700–£1,500/day and are used for large commercial pours. For domestic projects, always check whether barrow access is feasible before committing to pump hire.
Finding a reliable ready-mix GEN3 concrete supplier in the UK in 2026 involves several steps. First, identify local batching plants using the British Ready Mixed Concrete Association (BRMCA) member finder or by searching online for “ready mix concrete near me”. Major national suppliers include Tarmac, Aggregate Industries, Hanson (now part of Heidelberg Materials), and CEMEX, but many regions have independent local plants with competitive pricing. Always: obtain at least three quotes specifying the same GEN3 / C20 mix, slump class (S3), and aggregate size (20mm); confirm the plant’s minimum load and short-load surcharge policy; ask for a copy of the plant’s BS EN 206 / BS 8500 conformity declaration; confirm delivery lead time (typically 24–48 hours’ notice for standard orders); and ensure you have adequate labour and equipment ready for the pour — wait-time charges start quickly once the truck arrives on site.
Additional GEN3 concrete resources 2026: The Concrete Society | British Ready Mixed Concrete Association | BSI – BS 8500 Standard | HSE – Construction Safety | Checkatrade – Find a Groundworks Contractor