Concrete Calculator
Enter the length, width and depth of a slab to see how much concrete to order, in cubic metres and yards.
What this tool does
A concrete calculator works out the volume of concrete a slab needs. Multiply the length, width and depth, convert to cubic metres or cubic yards, and add an allowance for waste. Enter the three dimensions and the calculator returns the amount to order and its approximate weight.
Calculates the volume of a rectangular slab from its length, width and depth in metric or imperial units.
Adds your waste allowance and converts to cubic metres, cubic yards and cubic feet, with an approximate weight.
How to use it
- Choose metric or imperial units.
- Enter the length and width of the slab.
- Enter the depth: in centimetres for metric, inches for imperial.
- Leave a waste allowance of about 10%, or change it.
- Read the amount to order and its weight.
Why use a concrete calculator
Works in metric or imperial and returns cubic metres, cubic yards and cubic feet together, because suppliers quote in different units. Ordering too little concrete halfway through a pour is a serious problem, and ordering too much is wasteful. A quick, consistent calculation with an allowance for waste gets the quantity about right.
Why we built it
We built the concrete calculator to return cubic metres, cubic yards and cubic feet together, because suppliers quote in different units and ordering short is expensive. Use the square footage calculator for the area first, and the gravel calculator for the base layer underneath.
If your task goes further, try the Paver Calculator and the Brick Calculator.
Who this tool is for
- Homeowners pouring a patio, path or shed base
- Builders and landscapers ordering ready-mix
- Students doing volume problems
When to use it
- Planning a patio, path, shed base or driveway.
- Ordering ready-mix from a supplier.
- Estimating the cost of a slab.
- Checking a quote against your own figures.
How it is calculated
Volume = length × width × depth, with depth converted to the same unit as the length. The waste allowance multiplies the volume by 1 + waste ÷ 100. Cubic metres × 1.308 gives cubic yards.
Worked example: 5 m × 3 m × 0.10 m is 1.5 m³. With 10% extra, order 1.65 m³, about 4 tonnes of concrete.
Ready-mix is ordered by volume. Concrete mixed from bags is ordered by bag yield, which differs by product - check the bag.
What you enter, and what you get back
| Item | Details |
|---|---|
| Units | Metric or imperial. |
| Length and width | In metres or feet. |
| Depth | In centimetres or inches. |
| Waste | Extra percentage to allow. |
| Result | Volume to order, in three units, and approximate weight. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Volume is 10 times too small | Depth was entered in metres. | Enter depth in centimetres or inches. |
| Slab is not rectangular | The formula assumes a rectangle. | Split it into rectangles and add. |
| Quote differs | The supplier adds a minimum load or rounds up. | Ask for their minimum order. |
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Units | Metric (metres, depth in cm) |
| Length | 5 |
| Width | 3 |
| Depth / thickness | 10 |
| Extra for spillage and uneven ground | 10 % |
With those inputs, the calculator returns:
- Concrete to order: 1.65 m³
- Exact volume: 1.50 m³
- In cubic yards: 2.16 yd³
- In cubic feet: 58.3 ft³
- Approx. weight: 4.0 tonnes (8,730 lb)
Assumptions and limitations
- Rectangular slabs only.
- Does not model footings, steps or reinforcement.
- Weight uses about 2,400 kg per m³.
- An estimate - confirm quantities with your supplier.
Frequently asked questions
How do I calculate how much concrete I need?
Multiply the length, width and depth, with the depth in the same unit, then add about 10% for waste. The calculator does the conversions.
How much does a cubic metre of concrete weigh?
About 2,400 kg, or roughly 2.4 tonnes.
How thick should a concrete slab be?
Light paths are often 75 to 100 mm and driveways 100 to 150 mm, but the right thickness depends on the load and ground. Check local guidance.
How much waste should I allow?
About 5% to 10% is common, more for uneven ground or hand-mixed concrete.
How do I convert cubic metres to cubic yards?
Multiply by 1.308. The calculator shows both.