Free Volume, Materials & Cost Estimator – Updated 2026 Prices
Enter your application dimensions to calculate the required volume of GEN 0 concrete, the quantities of cement and aggregate needed, the number of 25 kg bags required, and the estimated material cost. GEN 0 is the lowest strength designation in the BS 8500 concrete classification system — suitable for mass fill, kerb bedding, blinding layers, and other non-structural, non-load-bearing applications.
GEN 0 concrete is the lowest strength designation in the BS 8500-1:2015 + A2:2019 (Concrete – Complementary British Standard to BS EN 206) classification system used throughout the UK construction industry. The GEN (General) series covers concrete mixes for non-structural, general-purpose applications where high compressive strength is not required. GEN 0 has a characteristic compressive strength of approximately 10 N/mm² at 28 days — significantly weaker than structural concrete grades such as C25 or C30, but entirely adequate for the range of applications it is designed for.
The equivalent site-mixed designation for GEN 0 is ST2 (Standard Mix 2) under the older BS 5328 system, which specified a nominal mix ratio of 1:3:6 by volume (one part Portland cement, three parts sharp sand, six parts 20mm coarse aggregate). This mix ratio remains a widely understood reference for site-mixed GEN 0 concrete in the UK in 2026. An alternative simplification using all-in ballast (pre-blended sand and gravel) gives a ratio of approximately 1:5 (cement:ballast) — a convenient shorthand for many small domestic and garden projects.
GEN 0 concrete is not suitable for structural applications. It should not be used for house foundations, structural floor slabs, reinforced concrete, or anywhere that load-bearing performance is required. For those applications, GEN 3 (C16/C20), RC25/C25, or higher grades must be specified. GEN 0's role is specifically in mass-fill, blinding, bedding, and non-structural oversite applications where the concrete serves primarily as a stable, level, non-compressible working surface or filler rather than a structural element.
GEN 0 concrete is appropriate for the following applications in UK construction in 2026:
GEN 0 concrete can be mixed on site from individual constituents or from all-in ballast. The standard mix ratios for GEN 0 / ST2 concrete in the UK are:
When mixing GEN 0 on site, always add water gradually — the mix should be workable enough to compact into the formwork or trench without excessive effort, but should not be so wet that it slumps or segregates. A mix that is too wet produces weaker, more porous concrete. The slump test (BS EN 12350-2) measures workability — for most GEN 0 applications, a slump of 50–100mm is appropriate. For blinding and oversite work, a slightly wetter mix (100–150mm slump) may be specified to allow easy spreading and screeding.
The BS 8500 GEN series covers five concrete strength grades from GEN 0 to GEN 4, each appropriate for progressively more demanding non-structural and lightly structural applications. The table below summarises all GEN grades alongside the equivalent ST (Standard Mix) designation and typical UK applications.
| Grade | Old ST Designation | Nominal Mix (by volume) | Compressive Strength (28-day) | Typical Cost (ready-mix, per m³) | Typical Applications |
|---|---|---|---|---|---|
| GEN 0 | ST2 | 1:3:6 | ~10 N/mm² | £85–£120/m³ | Blinding, mass fill, kerb bedding, trench fill, post holes |
| GEN 1 | ST2 | 1:3:5 | ~15 N/mm² | £90–£130/m³ | Mass fill, strip foundations for low-rise buildings (restricted use) |
| GEN 2 | ST3 | 1:2.5:4 | ~20 N/mm² | £95–£140/m³ | Drainage works, garage floors (light use), steps |
| GEN 3 | ST4 | 1:2:4 | ~25 N/mm² | £100–£150/m³ | Strip foundations, garden walls, domestic ground floors, driveways |
| GEN 4 | ST5 | 1:1.5:3 | ~30 N/mm² | £110–£165/m³ | Reinforced slabs, structural foundations, exposed paving |
| RC25 / C25 | — | Designed mix | 25 N/mm² | £115–£170/m³ | Structural slabs, columns, beams, house foundations |
| RC30 / C30 | — | Designed mix | 30 N/mm² | £125–£185/m³ | Basement walls, exposed structural elements, commercial slabs |
| RC35 / C35 | — | Designed mix | 35 N/mm² | £140–£200/m³ | Precast elements, heavily loaded structures, bridge decks |
| Constituent | Quantity per m³ (separate mix) | Quantity per m³ (ballast mix) | Standard Bag Size | Bags per m³ |
|---|---|---|---|---|
| Portland Cement (CEM I) | 170 kg | 210 kg | 25 kg | 7 bags (sep.) / 9 bags (ballast) |
| Sharp Sand (fine aggregate) | 510 kg | — | 25 kg | 21 bags |
| 20mm Gravel (coarse aggregate) | 1,020 kg | — | 25 kg | 41 bags |
| All-in Ballast (20mm) | — | 1,680 kg | 25 kg | 67 bags |
| Water | ~180 litres | ~180 litres | — | — |
| Total Batch Weight | ~1,880 kg/m³ | ~2,070 kg/m³ | — | — |
Note: quantities above are for guidance only. Actual densities vary with aggregate source, moisture content, and mix method. Always measure by volume (bucket or gauge box) rather than by weight when site-mixing, as this is more practical and consistent on site.
| Supply Method | Cost per m³ (materials, 2026) | Minimum Order | Best For | Notes |
|---|---|---|---|---|
| Bagged all-in ballast + bagged cement (25 kg) | £180–£280/m³ | No minimum | Small volumes under 0.3 m³ | Most expensive per m³ but most convenient; widely available at DIY retailers |
| Bulk ballast (loose tipped) + bagged cement | £90–£140/m³ | Typically 0.5–1 tonne ballast | 0.3–2 m³ – medium domestic projects | Good value; requires site space for ballast heap; bulk delivery £50–£120 |
| Ready-mix GEN 0 / ST2 (truck delivered) | £85–£120/m³ | Typically 3–6 m³ | Larger pours over 2–3 m³ | Best value per m³ above minimum; delivery charge typically £150–£300; short unload window (30–45 min) |
| Mini-mix / volumetric mixer (delivered) | £110–£160/m³ | No minimum (pay per m³) | 0.5–5 m³ – where truck access is impractical | Mixed on site at point of delivery; no minimum order; more expensive than truck ready-mix but highly flexible |
| Pre-mixed post-fix / post-mix concrete (bags) | £220–£320/m³ | No minimum | Post holes and spot uses only | Poured dry into hole and wetted in situ; convenient but expensive; GEN 0–GEN 1 equivalent strength |
Find concrete suppliers UK 2026: CEMEX Ready Mix UK | Aggregate Industries | Hanson Concrete | Checkatrade – Find a Concreting Contractor | Builders' Merchant Finder
| Item / Extra | Typical Cost Range (2026) | Notes |
|---|---|---|
| Ready-mix delivery charge | £150–£300 per delivery | Typically included for orders over 5 m³; charged for smaller orders or long distances |
| Mini-mixer / volumetric truck call-out | £80–£150 call-out + per m³ rate | Flexible quantities; no drum washing charge; ideal for awkward access sites |
| Drum mixer hire (per day) | £40–£80/day | 130–150 litre drum mixer; suitable for up to 1 m³ per day with labour |
| Concrete pump hire | £350–£700/day + per m³ pumped | For sites where direct pour from truck is not possible; boom pump or line pump |
| Formwork / shuttering (per m²) | £8–£25/m² | Timber boards and stakes; required to contain concrete in slabs and oversite pours |
| Polythene DPM (damp-proof membrane) | £0.50–£1.50/m² | 1200-gauge poly sheet; placed on blinding before structural slab; prevents ground moisture rising |
| Concreting labour (pour and level, per m²) | £12–£30/m² | Pouring, tamping, screeding, and initial finishing; blinding layer takes less time than finished slab |
| Concrete skip / washout facility | £50–£150 | Ready-mix trucks must wash out on site; provide a dedicated area or pay for on-truck washout |
| Curing compound or polythene curing cover | £0.20–£1.00/m² | Prevents premature drying and surface cracking; essential in warm, windy, or sunny weather |
| Short-load surcharge (ready-mix) | £100–£200 per delivery under minimum | Most ready-mix plants charge a surcharge for orders below their minimum (typically 3–4 m³) |
| Saturday / weekend delivery surcharge | £50–£150 | Most ready-mix plants charge premium rates for weekend and bank holiday deliveries |
| Bulk aggregate delivery (per load) | £60–£150 | Loose tipped ballast, sand, or gravel; tipper truck delivery to site |
GEN 0 is the BS 8500 designation for the weakest general-purpose concrete mix. Its equivalent under the older BS 5328 system is ST2 (Standard Mix 2), with a nominal site-mixed ratio of 1:3:6 (cement:sand:coarse aggregate by volume). The characteristic compressive strength at 28 days is approximately 10 N/mm² — adequate for non-structural fill and bedding, but not for load-bearing applications.
GEN 0 concrete must never be used for structural applications. It is not suitable for house foundations (use GEN 3 minimum), reinforced concrete (use C25/RC25 minimum), floor slabs subject to foot or vehicle traffic (use GEN 3–GEN 4), or any application where the concrete is relied upon to carry structural load. Using too weak a mix for foundations or structural slabs is a common and serious mistake on UK self-build projects.
The most technically important use of GEN 0 concrete in UK construction is as a blinding layer — a 50–75mm layer poured over excavated formation level before the main structural slab. Blinding protects the DPM from puncture by sharp sub-grade materials, provides a clean working surface for reinforcement placement, and prevents sub-soil contamination of the structural concrete. A good blinding layer is essential to the quality of any reinforced ground floor slab.
A cubic metre of fully compacted GEN 0 concrete weighs approximately 1,880–2,000 kg depending on aggregate density and moisture content. This is useful for calculating vehicle loads, checking ground bearing capacity before pouring large volumes, and estimating skip or waste requirements. A standard ready-mix truck carries approximately 6–8 m³ (12,000–16,000 kg), and access routes must be capable of supporting the loaded vehicle weight.
Most UK ready-mix concrete plants have a minimum order of 3–6 m³ for GEN 0 / ST2. Orders below this minimum are possible but attract a significant short-load surcharge (typically £100–£200 per delivery). For volumes under 2 m³, a volumetric (mini-mix) truck is usually more economical — these mix concrete on site and charge per m³ actually used, with no minimum order.
The strength and durability of any concrete — including GEN 0 — is governed primarily by the water-cement ratio. Adding too much water is the most common site mixing mistake: it makes the concrete easier to pour and spread but dramatically reduces strength and increases porosity. For GEN 0 with a 1:3:6 mix, aim for a water-cement ratio of approximately 0.55–0.65 (roughly 0.55–0.65 litres of water per kg of cement). Add water gradually and stop when the mix is cohesive and workable.
GEN 0 concrete achieves adequate strength for most purposes within 3–7 days under normal UK conditions (15–20°C). Full 28-day strength is approximately 10 N/mm². In cold weather (below 5°C), curing slows significantly — at 2°C, concrete may take 3–4 weeks to reach the strength achieved in 3 days at 20°C. Never allow freshly poured concrete to freeze — ice crystal formation destroys the cement matrix and permanently weakens the concrete.
For small domestic projects, all-in ballast (a pre-blended mixture of sharp sand and 20mm gravel) is the most convenient aggregate for GEN 0 mixing. It simplifies the mix to just two constituents (cement and ballast) and is widely available in 25 kg bags and bulk. For larger pours where quality control matters more, specifying separate sharp sand and 20mm gravel gives better control over the aggregate grading and allows the mix proportions to be optimised.
When site-mixing GEN 0, always measure constituents by volume using a gauge box (a bottomless timber box of known volume, typically one-bag equivalent). Never measure by shovel count — shovels vary enormously in how much material they carry and lead to inconsistent mixes. A typical gauge box for a one-bag batch holds approximately 20 litres. For a 1:5 ballast mix, one gauge box of cement and five gauge boxes of ballast gives a consistent, repeatable GEN 0 mix.
Concrete and aggregate materials are subject to 20% standard rate VAT in the UK. Ready-mix concrete supplied to a new residential dwelling construction site is zero-rated for VAT under HMRC's new build relief — the ready-mix supplier should be informed this is a new build to apply the correct VAT treatment. Concrete supply to repair, extension, or renovation projects is always standard rated at 20%. Always confirm VAT treatment before accepting a quotation.
Admixtures are rarely used in GEN 0 concrete given its non-structural, low-specification role — but plasticisers can be useful for improving workability without adding excess water, and accelerators (such as calcium chloride — not for use in reinforced concrete) can be used to speed curing in cold weather. For most GEN 0 applications, admixtures are unnecessary and add cost without benefit. Always check admixture compatibility with the cement type being used.
The Aggregates Levy applies to commercially exploited virgin aggregate in the UK, currently at £2.03 per tonne (2026). This levy is already included in the price of aggregate quoted by builders' merchants and ready-mix plants — it is not an additional charge. Recycled aggregate (crushed concrete) and some marine dredged aggregates are exempt or partially exempt from the levy, which is why recycled aggregate can sometimes be cheaper than virgin gravel for non-structural applications like GEN 0 blinding.
| Application | Typical Thickness | Volume per 10 m² | Bags (25kg ballast) per 10 m² | Notes |
|---|---|---|---|---|
| Blinding layer (over formation) | 50–75mm | 0.50–0.75 m³ | ~35–53 bags ballast + 7–10 bags cement | 50mm minimum; 75mm if sub-grade is uneven |
| Oversite concrete (non-structural) | 100mm | 1.00 m³ | ~67 bags ballast + 9 bags cement | Under structural slab; above compacted hardcore |
| Kerb bedding layer | 100mm bed + 150mm backing | 0.25–0.35 m³ per 10m run | ~17–24 bags ballast + 3–4 bags cement per 10m | Stiff mix required (low slump); DTP specification Class ST2 |
| Trench / void fill | Full trench depth | Varies by trench size | Calculate by volume | Self-compacting if mix is fluid enough; no vibration needed |
| Fence post hole (100mm dia.) | 600mm deep | ~0.005 m³ per hole | ~0.3 bags ballast + 1 bag post-mix (approx.) | Most practical to use pre-mixed post-fix bags for single posts |
| Fence post hole (200mm dia.) | 800mm deep | ~0.025 m³ per hole | ~2 bags ballast + 0.4 bags cement per hole | For larger posts and gate posts; ensure post is plumb before concrete sets |
| Lean-mix sub-base (path) | 100–150mm | 1.0–1.5 m³ per 10 m² | ~67–100 bags ballast + 9–14 bags cement | Stiff lean mix; laid and compacted; no reinforcement needed |
| Mass fill (redundant cellar / void) | Full void depth | Varies by void | Calculate by volume | Ready-mix most practical for large voids; pump access may be needed |
All quantities include a 10% wastage allowance. Bag quantities are approximate — actual requirements depend on aggregate density, moisture content, and exact mix proportions. For volumes above 1 m³, bulk aggregate delivery or ready-mix concrete will be significantly more cost-effective than bagged materials.
GEN 0 concrete is used for non-structural, non-load-bearing applications in UK construction. The most common uses are blinding layers (a 50–75mm layer poured over formation level before structural work), mass fill and trench filling, kerb bedding and backing, non-structural oversite concrete beneath floor slabs, post hole and fence post setting, and lean-mix sub-base layers beneath paths and light paving. GEN 0 is not suitable for structural foundations, reinforced slabs, or any application requiring significant compressive strength — for those purposes, specify GEN 3, C25, or higher.
The standard mix ratio for GEN 0 / ST2 concrete is 1:3:6 by volume — one part Portland cement, three parts sharp sand, and six parts 20mm coarse aggregate. Using all-in ballast (a pre-blended sand and gravel mix), the simplified ratio is 1:5 (cement:ballast). By weight, a cubic metre of GEN 0 requires approximately 170 kg cement, 510 kg sharp sand, and 1,020 kg coarse aggregate (or 210 kg cement and 1,680 kg ballast), plus approximately 180 litres of water. Always add water gradually to achieve a workable but firm consistency — do not over-water.
GEN 0 / ST2 ready-mix concrete costs approximately £85–£120 per m³ for a truck-delivered ready-mix in 2026 (South East England), plus a delivery charge of £150–£300. Site-mixed from bulk ballast and bagged cement costs approximately £90–£140 per m³ in materials. Using bagged all-in ballast and bagged cement from a DIY retailer costs approximately £180–£280 per m³ — the most expensive option per m³ but practical for small volumes under 0.3 m³. For volumes between 0.3 and 2 m³, a volumetric (mini-mix) truck offers the best balance of price and convenience, typically at £110–£160 per m³ with no minimum order.
No — GEN 0 is too weak for shed bases, garage floors, or any floor slab subject to foot or vehicle traffic. For a shed base with light foot traffic, specify a minimum of GEN 3 (C16) at 100mm thickness. For a garage floor subject to vehicle loading, specify a minimum of GEN 4 / C25 at 150mm thickness, with A142 mesh reinforcement. Using GEN 0 for a floor slab will result in a surface that dusts, cracks under load, and deteriorates rapidly. The marginal cost saving over GEN 3 is not worth the significantly inferior performance.
For a standard 75mm GEN 0 blinding layer, you need approximately 0.075 m³ per m² of area (plus 10% wastage = 0.083 m³/m²). Using the ballast-and-cement method, that equates to approximately 6 bags of 25 kg ballast and 1 bag of 25 kg cement per m². For a typical 20 m² (4m × 5m) floor blinding area, you would need approximately 120 bags of ballast and 18 bags of cement — at which point ordering bulk aggregate and mixing with a hired drum mixer, or ordering a volumetric ready-mix truck, would be significantly more economical than using bagged materials.
The key difference is compressive strength and application suitability. GEN 0 achieves approximately 10 N/mm² at 28 days with a lean 1:3:6 mix; GEN 3 achieves approximately 25 N/mm² at 28 days with a richer 1:2:4 mix. GEN 3 is the minimum specification for domestic strip foundations, garden wall footings, and ground floor slabs. GEN 0 is appropriate only for blinding, fill, and bedding where no structural load is applied. The cost difference is typically £20–£40 per m³ for ready-mix. Never substitute GEN 0 for GEN 3 in foundation or slab applications — the strength reduction is significant and the consequences can be serious.
Hand-mixing GEN 0 concrete is practical for small volumes up to approximately 0.1 m³ (a typical one-bag mix). Lay a sheet of plywood or use a large mixing trough. Measure out the dry ingredients by volume using a gauge box or bucket: for a 1:5 ballast mix, combine one bucket of cement with five buckets of all-in ballast. Mix the dry ingredients thoroughly until the colour is uniform. Make a well in the centre, add approximately half the water, and work the mixture from the outside into the centre. Add remaining water gradually until the mix is workable. Never mix more than you can pour and compact in 30 minutes — GEN 0 begins to stiffen as the cement hydrates.
GEN 0 concrete sets (becomes rigid and can no longer be worked) within approximately 2–4 hours of mixing at normal UK temperatures (15–20°C). However, setting is not the same as curing — the concrete continues to gain strength for weeks afterwards. Practical working strength (sufficient to walk on without damaging the surface) is typically reached within 24–48 hours. For blinding layers, this means structural work can usually proceed the day after pouring. Full 28-day strength (approximately 10 N/mm²) is reached in 28 days, though GEN 0's relatively low strength means this threshold is rarely the governing factor in when subsequent work can proceed.
The decision depends on volume and site access. As a general guide: for volumes under 0.3 m³, bagged materials mixed on site are most practical; for 0.3–2 m³, a volumetric (mini-mix) truck offers the best combination of price and flexibility; for volumes over 2–3 m³ with good vehicle access, a ready-mix truck is the most economical option. Ready-mix offers guaranteed mix consistency and quality that site mixing cannot always match, but imposes a short unloading window (typically 30–45 minutes) that requires adequate labour and preparation in advance. For blinding layers where a uniform depth and flat surface are important, ready-mix is generally preferred.
Adding excess water to concrete is the single most common mixing error on UK construction sites and has serious consequences even for low-specification GEN 0 mixes. Excess water reduces compressive strength (a w/c ratio of 0.7 instead of 0.6 can reduce strength by 30–40%), increases shrinkage cracking as the excess water evaporates during curing, increases porosity (making the concrete more permeable and frost-vulnerable), and causes segregation (aggregate sinks to the bottom, cement paste rises to the top). For GEN 0, the practical test is that the mix should hold its shape when squeezed in the hand but should not be crumbly — if it flows freely, it is too wet.
GEN 0 concrete has limited frost resistance compared to higher-grade mixes, due to its relatively high water-cement ratio and resulting porosity. Fully cured GEN 0 concrete in a buried or covered location (such as a blinding layer or trench fill) is generally not at significant risk from frost attack, as sub-ground temperatures rarely drop below freezing in UK conditions. However, exposed GEN 0 surfaces (kerb bedding, surface blinding) can be vulnerable to surface scaling in repeated freeze-thaw cycles. For any exposed application in an aggressive environment, specify GEN 3 or higher. Never pour fresh GEN 0 concrete when ground temperature is below 2°C without frost protection measures.
Additional resources for GEN 0 concrete UK 2026: CEMEX UK – Ready Mix Concrete | Aggregate Industries | BSI – BS 8500 Concrete Standard | The Concrete Centre | Checkatrade – Concreting Contractors