Free Concrete Calculators

Work out how much concrete your slab, pad or block wall needs. Every calculator shows its formula and a worked example.

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Planning a patio, driveway, shed base or block wall? These free concrete calculators help you measure the job, estimate how much material to order and what it may cost.

Concrete calculators

Cubic Yard CalculatorConvert length, width and depth into cubic yards — concrete is sold by the yard. Concrete Yard CalculatorCubic yards for slabs, footings, walls and columns, plus bags and weight. Concrete Slab Cost CalculatorVolume and budget for patios, driveways and garage floors. Concrete Bag CalculatorHow many 40, 50, 60 or 80 lb bags for slabs, fence posts and columns. Concrete Block CalculatorBlock count for walls, with openings and waste.

How to calculate concrete

The formula

Length × width × thickness (all in feet) = cubic feet.
Cubic feet ÷ 27 = cubic yards.
Add 5 to 10 percent for waste.

Example: a 12 × 10 ft patio, 4 inches thick: 12 × 10 × 0.333 = 40 cu ft. 40 ÷ 27 = 1.48 cu yd. With 10% waste, order about 1.63 cu yd.

Slab size to cubic yards

Slab size	4 in thick	6 in thick
10 × 10 ft	1.23 cu yd	1.85 cu yd
12 × 12 ft	1.78 cu yd	2.67 cu yd
16 × 16 ft	3.16 cu yd	4.74 cu yd
20 × 20 ft	4.94 cu yd	7.41 cu yd

Figures are net volume. Add waste before ordering.

Bags per cubic yard

Bag size	Yield per bag	Bags per cu yd
80 lb	0.60 cu ft	about 45
60 lb	0.45 cu ft	about 60
50 lb	0.375 cu ft	about 72

Yields vary by brand, so check the bag label.

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Concrete calculator FAQs

How do I calculate how much concrete I need?

Multiply length by width by thickness, all in feet, to get cubic feet. Divide by 27 to get cubic yards, then add 5 to 10 percent for waste.

How much concrete do I need for a 10 by 10 slab?

A 10 ft by 10 ft slab that is 4 inches thick needs about 1.23 cubic yards. With 10 percent waste, order about 1.36 cubic yards.

How many bags of concrete are in a cubic yard?

About 45 bags of 80 lb mix, 60 bags of 60 lb mix or 72 bags of 50 lb mix. Yields vary by brand, so check the bag label.

How thick should a concrete slab be?

Patios and walkways are commonly 4 inches thick. Driveways and heavy-load slabs are often 5 to 6 inches. Confirm with your contractor or local code.

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Estimates are for planning only. Read our Disclaimer or contact us if you spot a mistake.