Concrete Calculator
Cubic yards, bags of any size and real cost — all from one calculator. Enter your slab and the numbers update as you type.
Waste & region
Order extra for spillage & uneven subgrade. 10% is typical.
Concrete needed (10% waste in)
5.43 yd³
4.94 yd³ of concrete + waste · 400 sq ft
Bags of concrete needed (rounded up)
245
80 lb
326
60 lb
392
50 lb
489
40 lb
- Ready-mix (delivered)
- $739 – $1,207
- Bagged mix (80 lb, DIY)
- $1,348 – $2,205
- Installed by a pro
- $2,200 – $4,800
Estimate only — not a quote. Bag counts are rounded up and include a 10% waste allowance.
You'll also need
Sized for this exact slab — tap any item to open its calculator with your measurements already filled in.
Volumes use standard bag yields and a 10% waste allowance; costs are national US averages that vary by region, mix and finish. See our methodology for exactly how each figure is worked out, or check the reference sources:
The only concrete calculator you need
Most concrete calculators stop at cubic yards. SlabCosts gives you the three numbers that actually decide your job: how much concrete to order, how many bags if you're mixing by hand, and what it costs — whether you buy bags, order ready-mix, or hire a pro.
How it works
- Volume — width × length × thickness ÷ 27, with a 10% waste allowance built in.
- Bags — computed at 40, 50, 60 and 80 lb yields and always rounded up (you can't buy half a bag).
- Cost — bagged mix, ready-mix delivered, and fully installed, as an honest low–high range.
Everything runs in your browser — nothing you type is sent anywhere — and every result carries your measurements straight through to the base-gravel, rebar and cost calculators so you never re-type a number.