Convert cubic feet to cubic yards and back. Divide by 27 — with a conversion table, worked examples and what it means for ordering.
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yd³ = ft³ ÷ 27
Divide cubic feet by 27 to get cubic yards, and multiply by 27 to go the other way. A yard is three feet, so a cubic yard is 3 × 3 × 3 = 27 cubic feet. The figure is exact by definition, not a rounded conversion.
Worked example: 100 cubic feet ÷ 27 = 3.70 cubic yards. Going back, 3.70 × 27 = 100 cubic feet.
Cubic feet come out of the tape measure; cubic yards are what the supplier bills. Converting between them is a single division by 27 — but it is also where most ordering mistakes start, because the same calculation is easy to get twelve times wrong.
| Cubic feet | Cubic yards |
|---|---|
| 1 ft³ | 0.037 yd³ |
| 5 ft³ | 0.185 yd³ |
| 10 ft³ | 0.370 yd³ |
| 27 ft³ | 1 yd³ |
| 50 ft³ | 1.852 yd³ |
| 100 ft³ | 3.704 yd³ |
| 135 ft³ | 5 yd³ |
| 270 ft³ | 10 yd³ |
A yard is three feet. A cubic yard is therefore a cube three feet on each side: 3 × 3 × 3 = 27 cubic feet. Unlike most unit conversions this one is exact — it falls straight out of the definition, so there is no rounding to carry through your arithmetic.
Picture it as 27 one-foot boxes stacked three high, three wide and three deep. That mental image is also the quickest way to sanity-check a result: if a slab is clearly bigger than a few of those cubes, the answer in yards should be a small number, not a large one.
By far the most common error is leaving depth in inches.
A 20 × 10 ft slab at 4 in deep is not 20 × 10 × 4 = 800 ft³. Depth has to be in feet, and 4 in is 4 ÷ 12 = 0.333 ft. The real figure is 20 × 10 × 0.333 = 66.7 ft³, or 2.5 cubic yards. The wrong version is twelve times too large — a mistake big enough to order a full truck for a job that needs a third of one.
The rule: every measurement in the same unit before you multiply. Inches to feet, divide by 12. Then divide the result by 27.
Convert precisely, then round up when you order. Suppliers batch in fixed increments — often quarter-yards — so a calculated 3.70 yd³ becomes 3.75 or 4 on the docket. Add your waste allowance before rounding, not after: 3.70 with a 10% buffer is 4.07, which rounds to 4.25.
Rounding down to save money is a false economy. Being a quarter-yard short mid-pour means a cold joint or an emergency second load, and both cost far more than the concrete you saved.
Starting from dimensions rather than a volume? The cubic yard calculator goes straight from length, width and depth. Buying in bags? The concrete bag calculator converts a volume into a bag count. To price it up, use the concrete cost calculator with your supplier’s rate.
Pouring a different shape? These cover the rest of the common jobs.
Calculate the concrete volume for a rectangular slab from length, width and depth. Imperial and metric units, with a 10% waste buffer per ACI 318.
Calculate the concrete volume for a circular slab from diameter and depth. Imperial and metric units, with a 10% waste buffer per ACI 318.
Calculate the concrete volume for an irregular slab from a pre-measured area and depth. Imperial and metric units, with a 10% waste buffer per ACI 318.
Calculate the concrete volume for a circular column from diameter and height. Imperial and metric units, with a 10% waste buffer per ACI 318.
Calculate the concrete volume for fence-post holes — by hole, total across all holes, with post-profile displacement and a 10% waste buffer.
This tool is web-only. The Concrete Calculator app covers the five volume calculators — rectangular and circular slabs, irregular slab area, circular columns and post holes — with saved projects, job history and full offline use.
Free · 4.8 ★ on the App Store
