Free contractor calculator
Concrete Calculator
Enter your slab or footing dimensions and a thickness, and this calculator returns the volume of concrete in cubic feet and cubic yards, plus how many bags it takes if you're mixing by hand. The math is the same geometry JobPlumb's takeoff runs when you trace a slab on a real plan.
Your measurements
Result
- Concrete to order
- 31.11cu yd
- Volume
- 800cu ft
- Bags (80 lb)
- 1,400bags
How this is calculated
Volume
length (ft) × width (ft) × thickness (in ÷ 12) = cubic feet
Cubic yards
cubic feet ÷ 27, then × (1 + waste %)
Bags
cubic feet × (1 + waste %) ÷ 0.6 cu ft per 80 lb bag, rounded up
Taking this off a real plan?
JobPlumb measures slabs, walls, roofs and runs straight off your drawings, then prices the job and sends a proposal your client accepts online. Free to start, no install.
See JobPlumb estimatingHow to use it
- 1Pick a slab or footing and enter the length, width and thickness in feet and inches.
- 2Set a waste allowance (5% is typical for ready-mix).
- 3Read the volume in cubic yards to order from your supplier.
- 4If you're mixing on site, choose a bag size to see how many bags it takes.
Concrete Calculator, answered
One cubic yard is 27 cubic feet. An 80 lb bag of concrete mix yields about 0.6 cubic feet, so it takes roughly 45 eighty-pound bags to make a cubic yard, which is why ready-mix is cheaper past a few yards.
Measure it off the real plan in JobPlumb.
Free to start. No install, no sales call. Works in any browser.