Concrete Calculator

A concrete calculator turns the dimensions of your pour into the two numbers that actually matter at the supplier: how many cubic yards (or cubic metres) of ready-mix to order, and how many bags it would take if you are mixing by hand. Pick your pour type, enter the measurements, and the result updates instantly — including a 10% waste allowance so you are not caught short mid-pour.

Your measurements

Result

This is the hub for every concrete shape on ProjectFigure. If you know you are pouring one specific thing, the dedicated slab, footing, driveway, stairs, column, wall and sonotube calculators below ask only for the measurements that shape needs and add notes specific to it.

How it is calculated

Volume is your dimensions converted to a common unit and multiplied; a round column uses π·r²·height. Ready-mix is sold by the cubic yard in the US and the cubic metre almost everywhere else. An 80 lb bag of mix yields about 0.6 ft³ (0.017 m³) and a 60 lb bag about 0.45 ft³. We add 10% for waste because spillage, an uneven sub-base and slight over-excavation are normal on real pours.

Steps

Choose your pour type — slab, strip footing, round column or wall.
Enter the dimensions in feet and inches (or switch to metric, top right).
Read the headline figure: cubic yards or cubic metres of ready-mix.
Use the 10%-waste line when you place the order — that is the number to give the supplier.
Below half a cubic yard, check the bag counts instead; bagged mix is usually easier than a delivery.

Worked example

A 20 ft × 12 ft slab at 4 inches thick is 240 sq ft × 0.33 ft = about 80 cubic feet, or 2.96 cubic yards. With the 10% waste allowance you would order roughly 3.3 cubic yards of ready-mix.

Common questions

How much extra concrete should I order?

About 10% over the exact volume. Running short part-way through a pour creates a cold joint, which is far more expensive to deal with than a little leftover mix.

Should I use bags or ready-mix?

Under roughly half a cubic yard, bags are simplest. Above that, a ready-mix delivery is cheaper per yard and much faster than mixing dozens of bags by hand.

What thickness should a slab be?

Four inches suits patios, shed bases and footpaths. Driveways and anything carrying vehicle weight are usually five to six inches over a compacted base.

Does the calculator include rebar or mesh?

No — it sizes the concrete itself. Most slabs and footings are reinforced with steel mesh or rebar, which you size separately based on the structural design.