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Concrete Grade Selector — Application Lookup & Specification
Select the correct concrete grade, designation, slump class and exposure class for your application.
Optional — used only for the cost estimate
Delivered ready-mix — UK 2026 typically £110-145/m³
Safety notice
Structural elements must be designed or checked by a structural engineer before construction. Treat these figures as initial guidance for planning and budgeting, not a structural design.
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How We Calculate This
This tool selects the appropriate concrete grade, designation, exposure class and sulphate requirements based on the intended application.
Grade selection
Concrete grades are specified to BS 8500-1:2023.
The grade (C25, C30 etc.) indicates the characteristic compressive strength at 28 days in N/mm². The designation (GEN, ST, RC, PAV) indicates the application and durability requirements.
Sulphate class
Sulphate class is determined from soil investigation and BRE SD1. Classes range from DS-1 (low) to DS-4 (very high). Higher classes require sulphate-resistant cement types.
Frequently Asked Questions
Standard domestic foundations use C25/30 concrete (RC 25/30 or FND 2 designation to BS 8500-1:2023 — GEN 3 (C16/20) is the highest general mix, so C25/30 moves into the designated RC/FND series). The BS 8500 durability minimum for C25/30 at exposure class XC2 is 280 kg/m³ cement at max water/cement 0.60; many FND mixes are batched a little richer (≈300 kg/m³) for workability. In sulphate-bearing soils (common in clay areas), designated concrete DC-2 or higher is required. In contaminated ground, the structural engineer will specify a designed mix. Always check the soil investigation report for sulphate levels. Use our Concrete Mix Calculator for mix proportions or Concrete Volume Calculator for quantities.
GEN (General) mixes are for non-structural use like blinding, fill and garden work. ST (Standard) mixes are for structural applications like foundations and floor slabs. RC (Reinforced Concrete) mixes are specifically designed for reinforced concrete elements. PAV mixes are for external paving and driveways with freeze-thaw resistance.
Domestic driveways and hardstanding should use C28/35 PAV 1 concrete with air entrainment for freeze-thaw resistance (exposure class XF3). Standard GEN or ST mixes without air entrainment will scale and spall when exposed to frost. Where the surface is regularly treated with de-icing salts (XF4), step up to PAV 2 = C32/40. The PAV designations provide the durability needed for external paving (PAV 1 = C28/35, PAV 2 = C32/40 under the BS 8500 designated-concrete tables). Air entrainment cannot be added reliably by site mixing — order ready-mixed PAV.
Sulphate-resistant concrete uses cements that resist chemical attack from sulphates in the soil (common in clay soils). DS classes range from DS-1 (low, standard cement OK) to DS-4 (very high, requiring SRPC cement plus additional protection). A soil investigation determines the sulphate class. The BRE Special Digest 1 provides guidance.
Slump measures workability: S1 (10-40mm) = very stiff, S2 (50-90mm) = standard for slabs, S3 (100-150mm) = standard for foundations and pumped concrete, S4 (160-210mm) = flowing/self-compacting. For trench fill, S3 is standard. For floor slabs, S2 gives a stiffer mix that's easier to level. Never add water on site to increase slump.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.