About the Concrete Calculator
Getting a concrete order right matters: too little and the pour has a cold joint, too much and you pay for waste. This calculator works out the volume for the shape you are pouring, adds a waste allowance, and then breaks that volume down into cement bags, sand and aggregate for the mix ratio you choose.
Also known as: concrete volume calculator, how much concrete do i need, cubic meters of concrete, ready mix calculator, cement concrete calculator.
How to use this calculator
- Choose the shape you are pouring.
- Enter the finished dimensions in metres.
- Pick the mix ratio — M20 (1:1.5:3) suits most domestic slabs and footings.
- Order to the nearest quarter cubic metre above the figure shown.
Formula
Volume = length × width × depth (× π/4 × d² for round)
Worked example
Using the values pre-filled in the calculator above:
- What are you pouring?: Slab or footpath
- Length = 5 m
- Width = 4 m
- Thickness or depth = 0.1 m
- How many? = 1
- Mix ratio: 1 : 1.5 : 3 (M20) — 20 MPa — slabs and footings
- Waste allowance = 5 %
- Price per m³ (optional) = 140
the calculator returns:
- Concrete required: 2.1 m³
- Without waste: 2 m³
- In cubic yards: 2.747
- Cement bags (50 kg): 17
Working
5 × 4 × 0.1 = 2 m³ each× 1 and +5% waste = 2.1 m³
Tips & common mistakes
- Always round up. Running out mid-pour creates a weak cold joint.
- A 50 kg cement bag is about 0.035 m³ of loose powder.