Concrete Mix Calculator UK 2026
Instantly calculate cement, sand, aggregate, and water for your UK concrete project. Supports C20, C25, C30 grades and standard mix ratios.
Project Details
Enter your volume and select the appropriate UK concrete grade
Length × Width × Depth. We recommend adding 5% for wastage.
Material Requirements
Cement, sand, aggregate, and water for your mix
Enter your project volume and select a mix grade, then click Calculate Concrete Mix to see your materials.
UK Concrete Grades & Applications
Standard UK concrete mix classifications based on compressive strength (N/mm²) after 28 days of curing. Choosing the right grade is critical for structural integrity.
| Grade | Mix Ratio (C:S:A) | Strength (N/mm²) | Typical Application |
|---|---|---|---|
| C15 / GEN1 | 1 : 3 : 6 | 15 | Blinding concrete, non-structural fill |
| C20 / GEN3 | 1 : 2 : 4 | 20 | Domestic foundations, patios, internal floors |
| C25 / ST4 | 1 : 1.5 : 3 | 25 | Reinforced foundations, driveways, workshops |
| C30 / ST5 | 1 : 1 : 2.5 | 30 | Structural beams, commercial floors, piling |
| C35 | 1 : 1 : 2 | 35 | Heavy structural, high-rise, water retaining |
Concrete Mixing FAQ
Everything you need to know about mixing concrete in the UK, from standard ratios to building regulations.
For standard domestic foundations in the UK, a C20 (GEN3) mix is typically used. The standard volume ratio for C20 is 1:2:4 (1 part cement, 2 parts sharp sand, 4 parts aggregate). This provides sufficient strength for footings, patios, and internal floors.
For a standard C20 (1:2:4) mix, you will need approximately 12 to 13 bags of 25kg cement per cubic metre of wet concrete. For stronger mixes like C25 or C30, the cement content increases, requiring 16 to 18 bags per cubic metre.
The ‘C’ stands for Concrete, and the number represents its compressive strength in Newtons per square millimetre (N/mm²) after 28 days. C20 is suitable for domestic foundations and patios, C25 is used for reinforced foundations and driveways, while C30 is required for structural beams and commercial floors.
To calculate the volume in cubic metres (m³), multiply the length (m) by the width (m) by the depth (m). For example, a slab 4m long, 3m wide, and 0.1m deep requires 4 × 3 × 0.1 = 1.2 m³ of concrete. Always add 5-10% for wastage and over-site.
While DIY mixers often batch by volume using shovels or buckets, batching by weight is significantly more accurate and recommended for structural concrete. Water content is critical; adding too much water weakens the concrete, so always measure water carefully.