What does the Concrete Calculator do?

Calculate how much concrete you need in cubic metres or bags for slabs, footings, posts and columns. All calculations are performed in your browser using official UK rates and thresholds.

Does this include waste allowance?

Yes. Most building material calculations include a standard 10% waste allowance. You can adjust this figure depending on the complexity of your project and cutting requirements.

Material prices are indicative estimates based on average UK prices. Actual costs vary by region, supplier, brand and current market conditions. Always get quotes from local suppliers.

Concrete Calculator

Calculate how much concrete you need in cubic metres or bags for slabs, footings, posts and columns.

Last updated: April 2026 · Source: GOV.UK — Building Regulations Approved Document A

Shape

Length (mm)

Width (mm)

Depth (mm)

Volume

0.90 m³

Weight

2.16 tonnes

25kg Bags

20kg Bags

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Concrete volume is calculated by multiplying length × width × depth for rectangular slabs, or πr² × depth for circular areas such as post holes. The result in cubic metres tells you how much ready-mix to order, or how many bags of dry mix you need. A standard 25 kg bag of post-mix makes approximately 0.011 m³ of concrete.

For small jobs (under 1 m³), bagged dry-mix is practical. For larger pours, ready-mix delivery is more economical and ensures consistent quality. Most UK suppliers sell ready-mix in minimum loads of 1 m³ for mini-mix and 6 m³ for standard trucks. Add 5–10% for wastage.

Enter the dimensions of your slab, footing or post holes and the calculator shows volume in cubic metres, the number of 25 kg bags needed and an approximate cost estimate. For structural work like foundations, always check Building Regulations requirements and consider getting an engineer's specification for the concrete mix design.

Example: Garden shed base, 3 m × 2.4 m × 0.1 m deep

Volume: 3 × 2.4 × 0.1 = 0.72 m³
Add 10% wastage: 0.72 × 1.10 = 0.79 m³
Bags (25 kg post-mix): 0.79 ÷ 0.011 ≈ 72 bags
Or order 1 m³ ready-mix (typical minimum load)

Source: GOV.UK — Building Regulations Approved Document A

Frequently Asked Questions

What does the Concrete Calculator do?: Calculate how much concrete you need in cubic metres or bags for slabs, footings, posts and columns. All calculations are performed in your browser using official UK rates and thresholds.
Does this include waste allowance?: Yes. Most building material calculations include a standard 10% waste allowance. You can adjust this figure depending on the complexity of your project and cutting requirements.
Are prices accurate?: Material prices are indicative estimates based on average UK prices. Actual costs vary by region, supplier, brand and current market conditions. Always get quotes from local suppliers.