Free Mix Quantities, Bags & Ready-Mix Cost Estimator – Updated 2026 Prices
C20/25 concrete is a designed concrete mix specified under BS EN 206 and BS 8500, with a characteristic compressive cylinder strength of 20 N/mm² and a characteristic compressive cube strength of 25 N/mm² at 28 days. It is one of the most widely used concrete grades in UK domestic and light commercial construction, sitting above the GEN 3 standardised prescriptive mix in the concrete specification hierarchy and providing a well-defined, quality-assured concrete suitable for a broad range of structural and non-structural applications.
The designation C20/25 follows the European standard notation used in BS EN 206: the "C" denotes concrete, "20" is the characteristic cylinder strength in N/mm², and "25" is the characteristic cube strength in N/mm² — both at 28-day curing. In UK practice, the cube strength of 25 N/mm² is the more familiar value, as UK testing has historically used 150mm cubes. This grade is broadly equivalent to the old Grade 25 concrete under the superseded BS 5328 standard, and to the prescriptive GEN 3 / ST3 standardised mix under BS 8500-1.
Our C20/25 concrete calculator UK 2026 helps you estimate the volume of concrete required for any pour, then calculates either ready-mix order quantities, site-mix material weights (ballast, cement, water), or the number of pre-mixed bags required — along with estimated costs at current 2026 UK prices.
C20/25 is specified across a wide range of applications where a reliable, quality-assured concrete is required without the higher cost of stronger grades. In domestic construction, its most common uses are:
Understanding where C20/25 sits in the UK concrete grade hierarchy helps ensure you specify the right grade for your application. Using a grade that is too weak risks structural failure; over-specifying wastes money. C20/25 is appropriate for standard domestic foundations, ground-bearing slabs, and light vehicle areas. For reinforced suspended slabs, driveways with regular HGV access, or any application where durability in an aggressive environment is required, the stronger C25/30 or C28/35 grades should be specified. For heavy industrial floors or road construction, C32/40 or C35/45 is the norm.
It is important to note that a concrete grade specification is not complete without also specifying the exposure class under BS 8500. For a domestic ground-bearing slab in a non-aggressive indoor environment, exposure class XC1 (dry or permanently wet) applies and C20/25 with a minimum cement content of 240 kg/m³ satisfies the durability requirements. For external concrete exposed to freeze/thaw cycles, the minimum grade increases to C28/35 (XF1 exposure class) — meaning C20/25 is not suitable for external exposed slabs in the UK climate without additional protection.
Professional Concrete Resources 2026: The Concrete Centre UK | Hanson Ready-Mix UK | Breedon Group UK | Aggregate Industries UK
C20/25 concrete is most reliably produced by ordering a designed ready-mix from a batching plant, where mix proportions are computer-controlled to consistently achieve the specified 28-day strength. However, for smaller pours where ready-mix is not practical, an equivalent site-mixed concrete can be produced using a 1:2:4 (cement:sharp sand:20mm gravel) or 1:2:4 using all-in ballast at approximately 6 parts ballast to 1 part cement by volume — the standard GEN 3 site-mix equivalent.
For a site-mixed C20/25 equivalent, the following quantities are required per cubic metre of finished concrete:
Note that site-mixed concrete cannot be formally specified or certified as C20/25 under BS EN 206 — only designed mixes produced by a certified batching plant can carry the C20/25 designation. For work subject to building control inspection or structural engineer specification, ready-mix from a certified supplier with a delivery ticket confirming the mix designation is strongly preferable to site-mixing.
Ready-mix C20/25 concrete delivered by truck costs approximately £100–£130 per m³ (ex-VAT) in most parts of England in 2026, with prices in London and the South East typically 10–20% higher. The price includes the concrete itself and delivery in a standard mixer truck, but a short-load surcharge of £50–£150 is typically applied for orders below the minimum load (usually 4–6 m³). For smaller pours of 0.5–2 m³, the short-load surcharge can significantly increase the effective cost per m³. Pump hire — where a concrete pump is used to place concrete in difficult-to-access locations — costs an additional £250–£600 per day, depending on pump size and reach.
Prices vary between suppliers and regions. Always obtain at least two or three quotes from local ready-mix plants before placing an order. Most UK ready-mix suppliers provide a free online quote or phone estimate. Lead times in 2026 are generally short — 1–3 working days for standard orders — but always book in advance during busy periods (spring and summer). Confirm the delivery vehicle access requirements for your site: a standard mixer truck requires approximately 3.5m clear width and 4.0m clear height, plus a turning area or the ability to reverse in.
The table below places C20/25 in context with the full range of standard concrete grades used in UK construction, showing equivalent designations, typical applications, and 2026 ready-mix pricing.
| Grade (BS EN 206) | Cube Strength (28d) | BS 8500 Equiv. | Old Grade (BS 5328) | Typical UK Application 2026 | Ready-Mix Price/m³ 2026 |
|---|---|---|---|---|---|
| C8/10 | 10 N/mm² | GEN 1 | Grade 10 | Blinding, fill, non-structural | £85–£105 |
| C12/15 | 15 N/mm² | GEN 2 | Grade 15 | Mass fill, oversite blinding | £88–£108 |
| C16/20 | 20 N/mm² | GEN 3 | Grade 20 | Light foundations, paths | £92–£112 |
| C20/25 | 25 N/mm² | GEN 3 / ST3 | Grade 25 | Domestic foundations, slabs, driveways | £100–£125 |
| C25/30 | 30 N/mm² | RC25 / ST4 | Grade 30 | Reinforced slabs, driveways, garage floors | £105–£130 |
| C28/35 | 35 N/mm² | RC28 | Grade 35 | Exposed external slabs, frost-resistant | £110–£135 |
| C30/37 | 37 N/mm² | RC30 | Grade 37 | Structural elements, heavy-duty slabs | £112–£138 |
| C32/40 | 40 N/mm² | RC32 | Grade 40 | Industrial floors, HGV hardstandings, roads | £118–£145 |
| C35/45 | 45 N/mm² | RC35 | Grade 45 | Heavily loaded structural, ports, airports | £128–£158 |
| C40/50 | 50 N/mm² | RC40 | Grade 50 | High-rise, transfer structures, specialist | £140–£175 |
All ready-mix prices are 2026 UK averages (South East England base) exclusive of VAT, short-load surcharges, and pump hire. London prices are typically 10–20% higher. Always confirm live pricing with your local ready-mix supplier as prices vary with cement and fuel costs.
The table below sets out the full technical specification for C20/25 concrete in accordance with BS EN 206:2013+A2:2021 and BS 8500-1:2015+A2:2019 as applicable in the UK in 2026.
| Property | C20/25 Specification | Notes |
|---|---|---|
| Concrete designation | C20/25 | Cylinder / cube characteristic strength |
| Characteristic cylinder strength (fck) | 20 N/mm² | At 28 days; 5th percentile value |
| Characteristic cube strength (fck,cube) | 25 N/mm² | At 28 days; 150mm cubes |
| Mean cylinder strength (fcm) | 28 N/mm² | fck + 8 N/mm² per EN 1992-1-1 |
| Design tensile strength (fctd) | ~0.87 N/mm² | Used in shear and bond calculations |
| Modulus of elasticity (Ecm) | ~30 GPa | Secant modulus at 28 days |
| Density (normal weight) | ~2,350 kg/m³ | Fresh concrete; varies with aggregate |
| Max free water:cement ratio | 0.70 (XC1) / 0.60 (XC2) | Per BS 8500 exposure class requirements |
| Min cement content | 240 kg/m³ (XC1) / 280 kg/m³ (XC2) | Per BS 8500 Table A.3 |
| Max aggregate size | 20mm (standard) / 10mm (congested reinforcement) | Nominal maximum aggregate size |
| Target slump (workability) | S2 (50–90mm) or S3 (100–150mm) | S3 recommended for most domestic pours |
| Suitable exposure classes | XC1, XC2 (internal / ground contact) | Not suitable for XF1–XF4 (freeze/thaw) without air entrainment |
| Equivalent prescriptive mix | GEN 3 / ST3 (1:2:4 site mix) | Per BS 8500-2 Table A.3 |
| BS 8500 standardised mix equivalent | ST3 | For routine domestic applications |
| Manufacturing standard | BS EN 206:2013+A2:2021 | Specifying standard: BS 8500-1:2015+A2:2019 |
Concrete specification standards: BSI Group – BS EN 206 / BS 8500 | The Concrete Centre UK | GOV.UK Approved Documents
The table below provides a ready-reckoner for site-mixed quantities equivalent to C20/25 concrete. These quantities are based on the GEN 3 / 1:2:4 mix ratio, which is the site-mix equivalent of C20/25 under BS 8500. All quantities are per cubic metre of finished concrete and include a standard mix yield factor.
| Material | Quantity per m³ | Bags/Units (standard sizes) | 2026 Approx. Unit Cost | 2026 Cost per m³ |
|---|---|---|---|---|
| Ordinary Portland Cement (OPC) | ~310 kg | ~13 × 25kg bags | £8.50/bag | ~£110 |
| All-in Ballast (20mm all-in aggregate) | ~1,750 kg | ~2 bulk bags (850kg each) | £58/bulk bag | ~£116 |
| Sharp Sand (if mixing separately) | ~600 kg | Included in ballast or ~1 bulk bag | £55/bulk bag | ~£55 (if separate) |
| 20mm Gravel / Crushed Stone | ~1,150 kg | ~1.5 bulk bags (850kg each) | £62/bulk bag | ~£93 (if separate) |
| Water | ~170 litres | N/A | Negligible | ~£0 |
| Total Site-Mix Materials Cost | — | — | — | ~£226/m³ |
| Ready-Mix C20/25 (delivered) | — | — | — | £100–£125/m³ |
This comparison shows why ready-mix is generally more cost-effective than site-mixing for volumes over 1.0 m³ — even before accounting for the labour cost of site-mixing and the consistent quality advantage of a plant-produced mix. For small pours below 0.5 m³ where a short-load surcharge would apply to ready-mix, site-mixing or pre-bagged concrete may be more economical.
The table below provides recommended specifications for the most common UK construction applications using C20/25 concrete, along with minimum depths, sub-base requirements, and reinforcement guidance.
| Application | C20/25 Suitable? | Min Depth | Sub-base | Reinforcement | Notes |
|---|---|---|---|---|---|
| Domestic strip foundation | Yes ✓ | 200–300mm | Firm undisturbed ground | None (or as engineered) | Standard domestic spec; BCB approval needed |
| Trench fill foundation | Yes ✓ | Full trench depth | Firm undisturbed subsoil | None | Poured to within 150mm of ground level |
| Oversite / ground floor slab | Yes ✓ | 100mm | 150mm compacted hardcore + DPM | A142 mesh | Include DPM; Part C compliance |
| Shed / garage base | Yes ✓ | 100mm | 100mm MOT Type 1 | Optional A142 | Suitable for domestic use |
| Domestic driveway (cars only) | Yes ✓ | 125mm | 150mm MOT Type 1 | A142 or A193 | C25/30 preferred for better durability |
| External patio / path | Marginal ⚠| 100mm | 100–150mm MOT Type 1 | Optional A142 | Not frost-resistant; use C28/35 for exposed external |
| Garden wall footing | Yes ✓ | 200mm | Firm subsoil | None | Width = 3× wall thickness minimum |
| Fence / gate post hole | Yes ✓ | 600mm deep | N/A | None | Or use rapid-set for faster setting |
| Reinforced suspended slab | Marginal ⚠| 175mm+ | N/A – spanning | A393 + engineer design | C25/30 or stronger preferred; SE mandatory |
| External exposed slab (frost risk) | No ✗ | — | — | — | Use C28/35 min. for XF1 exposure class |
| Blinding concrete layer | Yes ✓ | 50–75mm | Compacted subsoil | None | GEN 1 / C8/10 cheaper if strength not required |
| HGV hardstanding / road | No ✗ | — | — | — | Use C32/40 minimum; full structural design required |
C20/25 denotes a concrete with a characteristic cylinder strength of 20 N/mm² and cube strength of 25 N/mm² at 28 days. The cube strength of 25 N/mm² is the more familiar value in UK domestic practice.
The GEN 3 / ST3 prescriptive site mix (1:2:4 cement:sand:gravel, or 6:1 all-in ballast:cement by volume) is the site-mixed equivalent of C20/25 under BS 8500-2.
Ready-mix C20/25 concrete costs approximately £100–£125/m³ (ex-VAT) delivered in most of England in 2026, with London and South East at the upper end. Short-load surcharges apply below minimum loads.
C20/25 is not suitable for external slabs exposed to freeze/thaw cycles (XF1–XF4 exposure). For external patios, paths, and driveways, specify C28/35 minimum, or use air-entrained concrete.
C20/25 reaches approximately 70% of its 28-day strength at 7 days under normal curing conditions (above 5°C, kept moist). Full design strength is achieved at 28 days under standard test conditions.
A C20/25 mix requires a minimum of 240 kg/m³ cement for XC1 exposure, rising to 280 kg/m³ for XC2. The site-mix equivalent uses approximately 300–320 kg/m³ of OPC.
Normal-weight C20/25 concrete has a fresh density of approximately 2,350 kg/m³ (2.35 tonnes/m³). This figure is used when calculating structural dead loads and delivery truck loads.
Most ready-mix suppliers apply a short-load surcharge of £50–£150 for orders below the minimum load (typically 4–6 m³). For small pours under 1 m³, site-mixing or bagged concrete is often more economical.
C20/25 is normally ordered at slump class S3 (100–150mm) for domestic pours, providing good workability around reinforcement. Request S2 (50–90mm) for unreinforced mass pours where a stiffer mix is acceptable.
Always add 10% to your calculated volume before ordering. Running out of concrete mid-pour creates a cold joint — a permanent weak plane — which building control will treat as a serious defect in structural elements.
For foundations and structural slabs, your building control officer will typically require a ready-mix delivery ticket confirming the C20/25 designation and conformance to BS 8500 / BS EN 206. Keep all delivery tickets.
Protect freshly placed C20/25 concrete from direct sun, wind, and temperatures below 5°C for a minimum of 3–7 days using polythene sheeting or curing compound to prevent plastic shrinkage cracking and ensure proper strength gain.
The use of C20/25 concrete in structural elements in the UK is governed by the Building Regulations 2010 (as amended) and the relevant British and European Standards. The following regulatory requirements are most relevant to domestic C20/25 concrete work in 2026.
Approved Document A requires that all structural concrete elements — including foundations, ground-bearing slabs that form part of a building, and columns — are designed and constructed to safely carry all loads. For domestic strip foundations, C20/25 (or equivalent GEN 3) concrete satisfies the material specification requirements of Approved Document A Table 10 for standard ground conditions. Building Control must inspect and approve all foundation concrete before it is covered — do not backfill foundations without the inspector's sign-off. Where piled or raft foundations are required due to poor ground conditions, a structural engineer's design specifying a higher-grade concrete (typically C25/30 or stronger) will be required.
Under Approved Document C, any ground-bearing concrete slab forming part of a habitable building must include a continuous damp-proof membrane (DPM) — typically 1200-gauge polythene — between the compacted hardcore sub-base and the C20/25 concrete. The DPM must lap with the damp-proof course (DPC) in the surrounding masonry walls. Where the ground has been identified as containing radon, methane, or other ground gases, additional protective measures (gas-resistant membranes, sub-slab venting) are required under Approved Document C before the concrete is placed.
Official Regulatory Resources: GOV.UK Approved Documents A & C | BSI Group – BS EN 206 / BS 8500 | NHBC Standards 2026 | The Concrete Centre UK
C20/25 concrete is used for a wide range of domestic and light commercial applications in the UK where a reliable, quality-assured concrete is required. The most common uses are domestic strip and trench fill foundations, ground-bearing floor slabs for house extensions and garages, domestic driveways (cars and light vans), garden wall footings, oversite concrete in new residential construction, and shed or outbuilding bases. It is not suitable for external exposed slabs in frost-risk areas (use C28/35 minimum) or for heavy vehicle hardstandings and roads (use C32/40 minimum).
C20/25 has a characteristic cube strength of 25 N/mm² at 28 days, while C25/30 has a characteristic cube strength of 30 N/mm² — 20% stronger. C25/30 also has a higher minimum cement content and lower maximum water:cement ratio, making it more durable, particularly in aggressive environments and frost-exposed locations. C25/30 is preferred for reinforced concrete slabs, external driveways, garage floors, and any application where the exposure class requires better durability than XC1. The cost difference between C20/25 and C25/30 ready-mix is typically only £5–£10/m³, making the upgrade to C25/30 very cost-effective for most applications.
The site-mixed equivalent of C20/25 is a GEN 3 / 1:2:4 mix (1 part cement : 2 parts sharp sand : 4 parts 20mm gravel by volume), or alternatively a 6:1 all-in ballast to cement mix by volume using pre-blended all-in aggregate. Per cubic metre of finished concrete, this requires approximately 310 kg of OPC cement (13 × 25kg bags), 1,750 kg of all-in ballast, and approximately 170 litres of water. Note that site-mixed concrete cannot formally carry the C20/25 BS EN 206 designation; only plant-produced ready-mix concrete with a certified conformity certificate can be specified as C20/25 for building control purposes.
Ready-mix C20/25 concrete costs approximately £100–£125 per m³ (ex-VAT) delivered in most of England in 2026. London and the South East are typically 10–20% more expensive. Most ready-mix suppliers apply a short-load surcharge of £50–£150 for orders below the minimum load (usually 4–6 m³). If your pour requires only 1–2 m³, the effective cost per m³ including the short-load charge can rise to £150–£200/m³, at which point site-mixing may be more economical despite the extra labour. Always get two or three quotes from local ready-mix plants and confirm lead times before booking.
C20/25 is suitable for a domestic driveway used by private cars and light vans only, at a minimum thickness of 125mm over a 150mm compacted MOT Type 1 sub-base with A142 or A193 mesh reinforcement. However, for driveways subject to more regular vehicle use, heavier vehicles (4x4s, commercial vans, pick-up trucks), or aggressive conditions including salt application in winter, C25/30 is a better choice as it provides greater durability and resistance to surface wear. C20/25 is also not rated for frost/thaw durability in fully exposed conditions — if your driveway is in a frost-risk area, specify air-entrained C28/35 or higher.
C20/25 concrete achieves approximately 50% of its 28-day strength at 3 days, 70% at 7 days, and 100% at 28 days under standard curing conditions (20°C, kept moist). In colder UK conditions (5–10°C), strength gain is slower — at 5°C, 28-day strength may take 6–8 weeks to fully develop. The concrete should not be loaded structurally until it has reached sufficient strength — typically a minimum of 7 days before placing significant loads on foundations, or 14–28 days before driving on a newly cast driveway. Keep the concrete protected from drying winds, direct sun, and frost during the critical first 3–7 days of curing.
Yes — any concrete foundation that forms part of a new building or extension requires Building Regulations approval under Part A (structural safety). You must notify your local authority Building Control Body (BCB) or an approved inspector before commencing foundation excavation, and the BCB must inspect the excavation and foundation concrete before it is covered. Your inspector will typically want to see the ready-mix delivery ticket confirming the concrete grade (C20/25 or equivalent), or if site-mixing, will assess the mix proportions visually. Do not backfill foundation trenches or place ground floor slabs over foundations without the inspector's approval at each stage.
Ready-mix C20/25 from a certified batching plant offers several significant advantages over site-mixing: consistent quality — computer-controlled batching ensures the mix meets the specified strength consistently; formal conformance — a delivery ticket confirms compliance with BS EN 206 / BS 8500, which building control requires for structural elements; cost-effectiveness for volumes over 1 m³ — despite the short-load surcharge for small orders, ready-mix is generally cheaper per m³ than site-mixing once labour is accounted for; and time saving — a ready-mix delivery places concrete much faster than site-mixing, reducing the risk of cold joints. For volumes under 0.5 m³ where short-load charges make ready-mix expensive, bagged concrete or site-mixing remains a practical alternative.
Slump (workability) class for C20/25 concrete should be specified based on the application. For most domestic pours — foundations, slabs, and driveways — specify slump class S3 (100–150mm target slump), which provides good workability for placing and compacting around reinforcement without being so wet that it segregates or bleeds excessively. For mass concrete foundations without reinforcement, S2 (50–90mm) is acceptable and will produce a slightly stronger, less permeable concrete. Never request the highest slump (S5 / self-compacting) for domestic structural applications as it involves excessive water content that reduces the 28-day strength significantly.
For a 4m × 3m × 0.15m slab: volume = 4 × 3 × 0.15 = 1.80 m³. Adding 10% wastage gives 1.98 m³ — round up to 2.0 m³ to order from a ready-mix supplier. At £110/m³ plus a short-load surcharge of approximately £80 (for under 4 m³), the total ready-mix cost would be approximately £300 ex-VAT delivered. If site-mixing, you would need approximately 620 kg of cement (25 bags), 3,500 kg of ballast (4 bulk bags), and 340 litres of water. Our calculator above computes all of these figures automatically from your dimensions.
C20/25 is generally marginal for suspended concrete floor slabs in standard domestic construction. While Eurocode 2 structural design can be carried out for C20/25, most structural engineers specify a minimum of C25/30 for suspended slabs due to the higher bending stresses, shear forces, and durability requirements compared to ground-bearing slabs. For any suspended slab, a structural engineer must design the slab, specify the concrete grade, reinforcement, cover, and formwork requirements. The small additional cost of upgrading from C20/25 to C25/30 (typically £5–£10/m³) is always worthwhile for suspended slab applications.
Normal-weight C20/25 concrete has a fresh density of approximately 2,350 kg per cubic metre (2.35 tonnes/m³). This figure is used when calculating the dead load of concrete elements for structural design, and when assessing whether delivery vehicles and site access can support the weight of a full concrete truck (typically 6–8 m³ capacity = 14–19 tonnes of concrete plus the truck's own weight of 15–20 tonnes, giving a total of approximately 30–40 tonnes gross vehicle weight). Always check that your site access road, bridge, or soft ground can support the loaded delivery vehicle before booking a ready-mix pour.
Additional Resources 2026: Ready-mix at Hanson UK | Breedon Group | Aggregate Industries | Concrete guidance at The Concrete Centre | Standards at BSI Group | Building regs at GOV.UK