Site Batch Concrete Mix Calculator
(C25 / ST2 Equivalent Guide)
Site Batch Concrete Mix Calculator (C25 / ST2 Equivalent Guide)
Estimate the materials required to mix concrete on site using a simple, practical guide based on a nominal C25 / ST2 mix. Enter the total volume of concrete required to calculate how much cement, sharp sand and aggregate you’ll need for your project.
This calculator is designed for general groundworks, patios, slabs and small-scale construction where site batching is suitable.
What Is a Site Batch Concrete Mix?
A site batch concrete mix refers to concrete that is mixed manually on site using individual materials such as cement, sand and aggregate, rather than being delivered pre-mixed from a supplier.
This method is commonly used for:
- Small concrete slabs
- Patio bases
- Footings and kerbing
- Repairs and minor works
A typical site mix is based on a 1:2:4 ratio (cement : sand : aggregate), which provides a general-purpose concrete suitable for many domestic and landscaping applications.
What Is C25 / ST2 Concrete?
C25 (also known as ST2) is a standard strength concrete widely used in the UK for:
- Domestic foundations
- Paving and patios
- Pathways and driveways
- General construction
It provides a balance of strength and workability, making it one of the most commonly used mixes in construction.
This calculator provides a site-mixed approximation of a C25-type mix, but it is important to understand that:
- Site-mixed concrete is not a certified or engineered mix
- Ready-mix concrete should be used for structural or critical applications
How This Calculator Works
The calculator takes your required concrete volume and:
- Applies a waste allowance
- Estimates material quantities based on a 1:2:4 mix ratio
- Converts materials into practical quantities such as:
- Cement (kg and bags)
- Sand (m³ and bulk bags)
- Aggregate (m³ and bulk bags)
This gives you a realistic guide for ordering materials and planning your job.
Important Notes
- This calculator provides estimates only
- Material densities and moisture content can vary
- Bulk bags are typically around 0.6m³, but may differ by supplier
- Always confirm quantities and specifications before ordering
Frequently Asked Questions
For a typical site mix:
- Cement: ~300kg (≈ 12 bags)
- Sand: ~0.45m³
- Aggregate: ~0.90m³
These values may vary depending on mix design and material conditions.
Approximately:
12–14 bags (25kg each) per cubic metre
This depends on mix ratio and waste allowance.
A 1:2:4 mix means:
- 1 part cement
- 2 parts sand
- 4 parts aggregate
This is a common general-purpose mix used for non-structural concrete applications.
You can for small domestic jobs, but for:
- Heavy loads
- Vehicles
- Long-term durability
Ready-mix concrete is strongly recommended.
C25 and ST2 refer to similar strength classes:
- C25 = design strength classification
- ST2 = prescribed mix used in the UK
Both are commonly used for general construction and paving applications.
A standard bulk bag typically contains:
Approximately 0.6m³
However, this can vary depending on supplier and material type.