MyRenoCalc

Concrete & masonry calculators

Concrete Calculator

The concrete truck is scheduled for Thursday and the supplier is asking how many yards you want. Guess low and the crew stands around while you panic-order more — and the seam where the second load meets the first never fully disappears. Guess high and you have paid roughly $150 per yard for concrete that hardens in the truck.

This calculator answers with real math. Enter your slab length, width, and thickness, add a waste allowance, and it gives you cubic yards rounded up to the nearest quarter-yard (how ready-mix is actually sold) plus the equivalent number of 80-lb bags if you are mixing by hand. Every figure traces to a manufacturer spec sheet, and the formula is shown with your own numbers below the results.

Your project, calculatedInstant results · Math shown
Volume
33.3 cu ft
Exact cubic yards
1.23 cubic yardsbefore waste allowance
Order this much
1.5 cubic yardswith 5% waste, rounded up to the nearest ¼ yard
Or in 80-lb bags
59 bagseach yields ~0.6 cu ft (Quikrete #1101)
How we calculate this (with your numbers)

Volume = 10 ft × 10 ft × (4 ÷ 12) in = 33.33 cu ft

Cubic yards = 33.33 ÷ 27 = 1.23 yd³

With 5% waste: 1.23 × 1.05 = 1.30 yd³ → rounded up to the nearest ¼ yard: 1.50 yd³

Bags (80 lb, 0.60 cu ft each): 35.00 ÷ 0.60 = 58.3 → always round up: 59 bags

How the math works

Worked example

A 10 × 10 ft patio slab, 4 inches thick, 5% waste allowance:

  1. Volume = 10 × 10 × (4 ÷ 12) = 33.33 cu ft
  2. Cubic yards = 33.33 ÷ 27 = 1.23 yd³
  3. With 5% waste: 1.23 × 1.05 = 1.30 yd³ → order 1.5 cubic yards
  4. Or in bags: 33.33 × 1.05 ÷ 0.60 = 58.3 → 59 eighty-pound bags

Enter these exact numbers into the calculator above and you will get the same result — that is the point. No black box.

Limitations

Frequently asked questions

Exactly 27. A cubic yard is a 3 ft × 3 ft × 3 ft cube. This calculator divides your slab volume in cubic feet by 27 to get cubic yards — the unit ready-mix trucks sell by.

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