Concrete Mix Ratios — UK Reference Guide
Getting the right concrete mix ratio is essential for strength, durability, and suitability for your application. This guide covers the standard mix ratios used in UK construction, from strong structural mixes to lean bedding mixes, with quantities per m³ and guidance on when to use each.
Standard Mix Ratios (Cement : Sand : Aggregate)
| Mix Ratio | Strength | Common Use |
|---|---|---|
| 1 : 1.5 : 3 | Very strong (~35 N/mm²) | Structural lintels, pre-cast items, heavy-duty floors |
| 1 : 2 : 3 | Strong (~30 N/mm²) | General structural: foundations, ground beams, reinforced work |
| 1 : 2 : 4 | Medium/strong (~25 N/mm²) | Foundations, oversite, driveways, garage floors |
| 1 : 2.5 : 4 | Medium (~20 N/mm²) | General purpose, paths, light-duty slabs |
| 1 : 3 : 6 | Lean (~15 N/mm²) | Oversite concrete, base for paving, mass fill |
| 1 : 8 (all-in ballast) | Weak (~10 N/mm²) | Fence post foundations, non-structural bedding |
Designated Mixes (BS 8500)
For ready-mix concrete ordered from a batching plant, you'll specify a designated mix under BS 8500. These are standardised mixes designed for specific applications:
| Designation | Strength Class | Application |
|---|---|---|
| GEN 0 | C6/8 | Blinding, kerb bedding, non-structural fill |
| GEN 1 | C8/10 | Strip foundations (no sulphates), oversite |
| GEN 2 | C12/15 | Blinding, oversite slabs, unreinforced mass concrete |
| GEN 3 | C16/20 | Paths, oversite, mass fill, unreinforced strip foundations (domestic) |
| FND 2 | C25/30 | Sulfate-resistant foundations (DC-2 exposure — most domestic foundations) |
| FND 3 | C28/35 | Higher-sulfate foundations (DC-3) |
| RC25/30 | C25/30 | Reinforced foundations, suspended floors (low exposure) |
| RC28/35 | C28/35 | Reinforced structural work, ground beams |
| RC 35 | C28/35 | Heavy structural, pre-stressed, commercial |
BS 8500 designations: GEN 3 (C16/20) for general domestic unreinforced strip foundations in low-sulfate ground; FND 2 (C25/30) for sulfate-resistant trench-fill (DC-2, most common). RC designations (e.g. RC25/30) apply to reinforced concrete by exposure class. Your structural engineer or building control will specify the required mix based on BS 8500 Table A.6 and AD-A.
Quantities Per m³
Approximate quantities of materials needed to produce 1 m³ of mixed concrete:
| Mix Ratio | Cement (25 kg bags) | Sharp Sand (kg) | Gravel/Aggregate (kg) |
|---|---|---|---|
| 1 : 2 : 3 | 14 bags (350 kg) | 700 kg | 1,050 kg |
| 1 : 2 : 4 | 11 bags (275 kg) | 550 kg | 1,100 kg |
| 1 : 2.5 : 4 | 10 bags (250 kg) | 625 kg | 1,000 kg |
| 1 : 3 : 6 | 8 bags (200 kg) | 600 kg | 1,200 kg |
Quantities are approximate due to moisture content and compaction. Always order 5–10% extra.
Site-Mixed vs Ready-Mix
For volumes over 1 m³, ready-mix from a batching plant is almost always more practical and ensures consistent quality. Minimum order is typically 1 m³ (some suppliers offer 0.5 m³ in a mini-mix truck). Ready-mix costs around £80–£120 per m³ delivered, depending on location and mix specification.
For smaller volumes, site mixing with a cement mixer, bags of cement, and loose aggregates is more cost-effective. One bag of cement (25 kg) makes approximately 0.07–0.08 m³ of concrete in a 1:2:4 mix.
Calculate Your Concrete Needs
- Concrete Mix Calculator — cement, sand, and aggregate for your chosen mix
- Concrete Volume Calculator — volume in m³ for foundations, slabs and paths
- Foundation Calculator — foundation depth, width and concrete volume
Mix ratios and quantities are based on UK industry standards and are provided for general guidance. Always follow structural engineer specifications for load-bearing work. Concrete mixes should comply with BS 8500 for structural applications.