Concrete Calculator
ft
ft
in
Cubic Yards1.23
Cubic Feet33.33
60-lb Bags75
This concrete calculator works out how much concrete a slab, footing, or column needs, reporting the volume in both cubic feet and cubic yards plus the number of 60-pound bags. You enter length and width in feet and depth in inches, and it converts everything to a consistent volume. Concrete is sold by the cubic yard for ready-mix and by the bag for small pours, so both figures are shown side by side.
Formula
cubicFeet = L × W × (depth/12); cubicYards = cubicFeet / 27; bags = ceil(cubicFeet / 0.45)
- L, W
- Length and width of the pour in feet
- depth
- Thickness of the pour in inches (divided by 12 to convert to feet)
- 27
- Cubic feet per cubic yard
How it works
- Enter the length and width of the pour in feet and the thickness (depth) in inches.
- The depth is converted from inches to feet (÷12), then multiplied by length and width to give the volume in cubic feet.
- Cubic feet are divided by 27 to get cubic yards, and divided by the yield of a 60-lb bag (about 0.45 cu ft) and rounded up to get the number of bags.
Worked example
A 10 ft × 10 ft slab poured 4 inches thick.
- Convert depth: 4 in ÷ 12 = 0.333 ft.
- Volume: 10 × 10 × 0.333 = 33.33 cubic feet.
- Cubic yards: 33.33 ÷ 27 = 1.23; bags: ceil(33.33 / 0.45) = 75.
About 1.23 cubic yards (33.33 cubic feet), or 75 sixty-pound bags.
Frequently asked questions
- Why is concrete measured in cubic yards?
- Ready-mix concrete is batched and delivered by the cubic yard, which equals 27 cubic feet. Knowing your yardage lets you order the right truck volume and compare it against bag counts for small jobs.
- How many 60-lb bags are in a cubic yard?
- Each 60-lb bag yields roughly 0.45 cubic feet, so a full cubic yard (27 cubic feet) takes about 60 bags. Bagged mixing is practical only for small pours; larger volumes are far cheaper as ready-mix.
- Should I order extra concrete?
- Yes, a little. Subgrade irregularities and spillage mean most pros add about 5-10% over the calculated volume so they do not run short mid-pour, since a cold joint from a second batch weakens the slab.
- Does it work for footings and columns too?
- Yes. Treat the footing or column cross-section as the length and width and its run or height as the depth. For round columns, compute the volume separately, since this tool assumes a rectangular shape.