Calculators
Concrete Calculator
Enter the size of your slab, footing, column, tube or steps to get the concrete to order in cubic yards or m³, plus how many premix bags to buy, with bag sizes for your country.
V = length × width × thickness
Calculated on your device — nothing is sent anywhere. Prices are yours to enter.
Works in your browser. No account needed.
Frequently asked questions
How many bags of concrete do I need?
Divide the volume by one bag’s yield and round up. QUIKRETE’s Concrete Mix data sheet gives about 0.30 ft³ for a 40 lb bag, 0.45 ft³ for 60 lb and 0.60 ft³ for 80 lb. A 10 × 10 ft slab 4 in thick is 33.3 ft³ (1.23 yd³), so it needs 56 of the 80 lb bags before any waste allowance — 62 with 10% extra.
How do I convert cubic feet to cubic yards?
Divide by 27, because a cubic yard is 3 ft × 3 ft × 3 ft. A cubic yard is exactly 0.764554857984 m³, and a cubic meter is about 1.308 yd³. Ready-mix is sold by the cubic yard in the US and by the cubic meter in most other countries; the calculator shows both.
What yields are used for metric bags?
Most metric premix bags don’t publish one standard yield, so 20, 25 and 30 kg bags use QUIKRETE’s own ratio — an 80 lb (36.2 kg) bag makes about 17 L, roughly 0.47 L per kg. The Australian 20 kg bag uses Cement Australia’s figure (two bags fill a 450 × 500 × 75 mm slab, about 8.4 L each). Every yield is editable, so type in the number printed on your bag.
How much extra concrete should I order?
Uneven ground, forms that bow and spillage mean a pour almost always takes more than the drawing says. An allowance of around 5–10% is a common starting point; use more for rough excavations. Running short in the middle of a pour is far worse than having a little left over.
How are steps calculated?
Each step is treated as a solid block from the ground up: step 1 is one rise tall, step 2 two rises, and so on, each one tread deep, except the top step, which uses the platform depth if you enter one. The sum is multiplied by the stair width.
Which countries are supported?
The US, Canada, the UK, Australia, India, Germany and the EU, and Türkiye. The country is guessed from your browser language and sets units, the currency symbol for prices you enter, and local bag sizes: 40/60/80 lb in the US, 25/30 kg in Canada, 20/25 kg in the UK and EU and 20 kg in Australia. In Türkiye and India, where concrete is usually ready-mix or mixed on site, it also shows 50 kg cement bags.
About this tool
This concrete calculator works out the volume for the pours that home projects and small jobs need: slabs, patios and floors (length × width × thickness), strip footings and walls, round columns and post holes, hollow tubes (round forms with a core), and solid steps. Long dimensions are entered in feet or meters and thin ones — thickness, footing width, diameter, rise and tread — in inches or centimeters, which avoids a classic mistake: multiplying feet by inches.
The result is the volume to order including a waste allowance, in cubic yards, cubic meters and cubic feet, alongside the bags of premixed concrete needed for each bag size. US bag yields come from the QUIKRETE Concrete Mix (No. 1101) data sheet: 0.30 ft³ per 40 lb bag, 0.45 ft³ per 60 lb and 0.60 ft³ per 80 lb. Metric presets use the same density or, for Australia, Cement Australia’s published coverage. Each yield can be edited, a custom bag can be added, and optional prices show the cost of bags or of ready-mix by the yard or cubic meter.
Local practice differs, so a country setting chooses sensible defaults. The US uses feet, inches and pound bags; Canada, the UK, Australia and the EU use metric bags; in Türkiye (where concrete is usually ordered as ready-mix, hazır beton, by the cubic meter) and in India, the calculator also estimates 50 kg cement bags for site-mixed concrete. The cement content is pre-filled with 300 kg/m³, the minimum IS 456 sets for reinforced concrete in mild exposure, and should be replaced with the figure from your mix design.
Bags make sense for small pours; beyond a cubic yard or so, dozens of 80 lb bags means a lot of mixing, and ready-mix delivery is usually worth pricing. Whatever you choose, order enough to finish in one continuous pour, check the thickness your local code or engineer requires, and keep in mind that the calculator gives quantities, not a structural design.