Plan your project

Concrete slab calculator

Estimate concrete slab volume in cubic yards or cubic metres, add an allowance, and compare material costs.

Materials / Concrete

Concrete slab calculator

Estimate the concrete needed for a rectangular slab.

01 / Concrete

Quick unit preset

Length

Width

Thickness

Extra allowance (%)

Cost currency

Supplier unit price (optional)

Use your supplier’s local price.

Price is per

Show main result in

Mix units freely. Changing a unit converts the entered value. For a new measurement, choose its unit first, then enter the number. Decimal feet: 10 ft 6 in = 10.5 ft.

Behind the result

Simple formula. Clear assumptions.

Volume = length × width × thickness
Order estimate = volume × (1 + extra % ÷ 100)

All dimensions are converted into consistent units before calculating. One cubic yard equals 27 cubic feet. One foot equals exactly 0.3048 metres. Results are rounded for display, not during calculation.

This tool assumes a uniform rectangular slab. It does not determine safe slab thickness, reinforcement, foundations, or compliance with building codes.

Each dimension has its own unit. Supplier pricing and the displayed volume can use different units. One yard is exactly 0.9144 metres; one litre is 0.001 cubic metres. Unit changes convert existing values and clear results until you calculate again.

Worked example

A 10 × 10 ft slab, 4 inches thick

10 × 10 × (4 ÷ 12) = 33.333 cubic feet.
Divide by 27 to get 1.235 cubic yards.
Add 10% extra to get approximately 1.358 cubic yards.

The 10% default is an editable planning assumption, not a universal recommendation. Site conditions and supplier order increments may change what you need to order.

Choose the currency of your supplier’s price, then use “Convert estimate to” for an exchange-rate comparison. Bag estimates will be added later using manufacturer-stated yield.

A quick walkthrough

How to use the concrete slab calculator

Choose an imperial or metric preset, or select a unit separately for length, width, and thickness. If you are entering a new measurement, select its unit first: changing a unit converts any existing value.
Enter the dimensions of a uniform rectangular slab. Set the extra allowance to suit the job rather than assuming the sample 10% is always appropriate.
For an optional cost estimate, select the supplier’s price currency, enter their unit price, and choose what that price is per. The price unit can differ from the main result unit.
Click Calculate quantity. Review the base volume, extra allowance, and total in your chosen units. Use Convert estimate to only if you want a reference currency comparison; recalculate after changing inputs.

Before you order

Frequently asked questions

Practical answers for this calculator. Select a question to read more.

How do I convert slab thickness from inches to feet?

Divide inches by 12. For example, 4 inches is 4 ÷ 12 = approximately 0.3333 feet. In this calculator you can simply select inches for thickness; it handles the conversion internally. Do not enter 4 feet when you mean 4 inches.

How much extra concrete should I allow?

The default 10% is an editable planning assumption, not a universal recommendation. Uneven ground, formwork, spillage, and placement conditions can affect the amount needed. Ask your supplier or contractor what allowance and order increment suit your job. The tool applies the entered percentage once to the base volume.

Can I mix feet, metres, and millimetres?

Yes. Each dimension has its own unit selector. For example, 10 feet × 3 metres × 100 millimetres gives a base volume of 0.9144 m³, or 1.00584 m³ with 10% extra. Changing a selector converts the existing measurement; select the unit first before typing a different measurement.

Does the estimate include delivery and labour?

No. Cost is the volume including your allowance multiplied by the entered supplier unit price. It does not automatically add labour, taxes, delivery, pumping, reinforcement, or minimum-order charges. Get a complete quote from your supplier.

Can this tool tell me the safe slab thickness or number of concrete bags?

No. You must supply the thickness; the tool does not design a structural slab or specify reinforcement. It also does not currently calculate bags. For bagged concrete, use the product’s stated mixed yield rather than assuming all bags of the same weight produce the same volume.

For more detail, read our methodology and disclaimer. Found a problem? Contact CalHomeGo.

Calculations run in your browser. Optional currency conversion contacts Frankfurter for rates; your measurements and cost amounts are not sent. Reference rates are not bank quotes.

Concrete slab calculator