Work out cubic yards from length, width and depth. Results in cubic yards, feet and metres, with a 10% waste buffer for ordering.
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Accepts 20ft 6in, 10' 6", 20.5, 4 1/2.
Enter length, width and depth to see the volume in cubic yards.
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yd³ = (length ft × width ft × depth ft) ÷ 27
Multiply length by width by depth with every measurement in feet, which gives cubic feet, then divide by 27 to get cubic yards. Depth is usually quoted in inches, so divide inches by 12 first — a 4 in slab is 0.333 ft.
Worked example: A 20 ft × 10 ft slab at 4 in deep is 20 × 10 × 0.333 = 66.7 ft³, and 66.7 ÷ 27 = 2.5 cubic yards.
Concrete, gravel, topsoil and mulch are all sold by the cubic yard in the United States, but nobody measures a slab in yards — you measure it in feet and inches. That mismatch is where ordering goes wrong. This calculator does the conversion and adds the 10% buffer you should be ordering to.
At the standard 4 in residential slab depth:
| Slab | Area | Cubic yards |
|---|---|---|
| 10 × 10 ft | 100 ft² | 1.23 yd³ |
| 12 × 12 ft | 144 ft² | 1.78 yd³ |
| 16 × 16 ft | 256 ft² | 3.16 yd³ |
| 20 × 20 ft | 400 ft² | 4.94 yd³ |
| 24 × 24 ft | 576 ft² | 7.11 yd³ |
Depth changes the answer proportionally: the same 20 × 20 ft slab at 6 in is 7.41 yd³ rather than 4.94. Half again the depth is half again the concrete, and it is the single easiest way to blow a budget without noticing.
A yard is three feet, so a cubic yard is 3 × 3 × 3 = 27 cubic feet. It is a definition, not a measured conversion, so dividing cubic feet by 27 is exact. The number that trips people up is not 27 but the depth: a 4 in slab is 0.333 ft, not 4, and entering 4 gives an answer twelve times too large.
The arithmetic is identical for gravel, road base, topsoil and mulch — length × width × depth ÷ 27. What changes is the buffer and the depth convention. Loose materials settle and compact, so suppliers often suggest more than 10% for base course, and mulch is usually spread 2 to 3 in deep rather than 4.
Weight per yard differs sharply too, which matters for delivery: concrete is about 4,000 lb per cubic yard, dry gravel roughly 2,800 lb, and mulch only a few hundred.
Converting a figure you already have? Use the cubic feet to cubic yards converter. Buying in bags rather than by the truck? The concrete bag calculator turns a volume into a bag count. Once you know the volume, the concrete cost calculator applies your supplier’s rate.
For a shaped pour rather than a plain rectangle, the circular slab, circular column and post hole calculators handle the geometry for you.
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
