Concrete Calculator

A 10 ft x 10 ft slab at 4 inches thick needs 1.23 cubic yards of concrete (33.3 cubic feet). That is 75 bags of 60 lb concrete mix (74.07 exact — round up, you cannot buy part of a bag), or 56 bags of 80 lb mix, before waste. Add 10% waste and order 1.36 cubic yards.

One cubic yard of concrete takes about 60 bags of 60 lb mix (each 60 lb bag yields about 0.45 cubic feet, and a yard is 27 cubic feet). For 80 lb bags it is 45 bags per yard, and for 40 lb bags it is 90 bags per yard.

4 inches is standard for patios, walkways and shed bases. Driveways and garage floors should be 5 to 6 inches, and anything carrying heavy vehicles or loads should be 6 inches or more on a compacted gravel base.

Multiply length x width x thickness in feet, then divide by 27. For example, 10 ft x 10 ft x 0.33 ft (4 inches) = 33.3 cubic feet, and 33.3 / 27 = 1.23 cubic yards.

Yes — order 10% extra. Uneven ground, spillage and form movement always use more concrete than the maths says, and running short mid-pour leaves a cold joint in the slab.

Work out the concrete cost, then add delivery and labour. For example, a 10 ft x 10 ft slab at 4 inches thick needs 1.36 cubic yards with 10% waste — at $150 per yard that is $203.70 of concrete. Add a $75 delivery fee and labour at $6 per square foot ($600 for 100 sq ft) and the installed total is $878.70. Enter your own prices in the calculator to price your job.