Concrete Calculator

US & Canada

Enter your measurements in feet or metres. You get the volume in cubic yards and cubic metres, plus how many bags that is, including the 30 kg bags sold in Canada.

Work out your concrete

ft
ft
in
%

Spillage, uneven ground and over-dig. 5–10% is typical.

Concrete needed

0 cubic yards

0 cubic metres · 0 cubic feet

Or buy bags

Bag Bags Pallets Sold in

Yields are the typical figures printed on ready-mix bags. Check the bag you are buying, because brands differ.

How the calculation works

Concrete is sold by volume, so every one of these pours comes down to the same thing: work out the space you are filling, then convert it into the units your supplier uses.

Slabs and footings

A slab is a box. Multiply the three measurements, keeping them all in the same unit, then convert:

  • Cubic feet = length (ft) × width (ft) × thickness (ft)
  • Cubic yards = cubic feet ÷ 27
  • Cubic metres = cubic feet ÷ 35.31

Thickness is the step people get wrong. A 4 inch slab is 4 ÷ 12 = 0.333 ft, not 4. And a cubic yard is 27 cubic feet, not 3. It is a cube three feet on every side.

Sonotube footings and round columns

A tube is a cylinder, so the diameter gets halved and squared:

  • Cubic feet = π × (diameter in ft ÷ 2)² × height (ft)

Doubling the diameter quadruples the concrete. A 12 inch tube takes four times as much as a 6 inch one at the same depth, which is why the jump from a 10 to a 12 inch tube costs more than it looks.

Post holes

A post hole is a cylinder with the post taking up part of it. The calculator subtracts the post, using its real dressed size rather than its name. A 4×4 is actually 3½ inches across, and a 6×6 is 5½.

Concrete for common slab sizes

Volumes include a 10% waste allowance, and bag counts are rounded up to whole bags.

Concrete needed for common slab sizes, with 10% waste
Slab Thickness Cubic yards Cubic metres 80 lb bags 60 lb bags 30 kg bags
8 × 8 ft 4" 0.87 0.66 40 53 53
8 × 8 ft 6" 1.3 1 59 79 79
10 × 10 ft 4" 1.36 1.04 62 82 82
10 × 10 ft 6" 2.04 1.56 92 123 123
10 × 12 ft 4" 1.63 1.25 74 98 98
10 × 12 ft 6" 2.44 1.87 110 147 147
12 × 12 ft 4" 1.96 1.5 88 118 118
12 × 12 ft 6" 2.93 2.24 132 176 177
10 × 16 ft 4" 2.17 1.66 98 131 131
10 × 16 ft 6" 3.26 2.49 147 196 196
12 × 16 ft 4" 2.61 1.99 118 157 157
12 × 16 ft 6" 3.91 2.99 176 235 236
16 × 20 ft 4" 4.35 3.32 196 261 262
16 × 20 ft 6" 6.52 4.98 294 392 392
20 × 20 ft 4" 5.43 4.15 245 326 327
20 × 20 ft 6" 8.15 6.23 367 489 490
24 × 24 ft 4" 7.82 5.98 352 470 471
24 × 24 ft 6" 11.73 8.97 528 704 706

Concrete per sonotube footing

One footing, including 10% waste. Multiply by how many you are pouring.

Concrete needed per sonotube footing, with 10% waste
Tube Depth Cubic feet Cubic metres 80 lb bags 60 lb bags 30 kg bags
8" tube 3 ft 1.15 0.03 2 3 3
8" tube 4 ft 1.54 0.04 3 4 4
10" tube 3 ft 1.8 0.05 3 4 5
10" tube 4 ft 2.4 0.07 4 6 6
12" tube 3 ft 2.59 0.07 5 6 6
12" tube 4 ft 3.46 0.1 6 8 8
16" tube 3 ft 4.61 0.13 8 11 11
16" tube 4 ft 6.14 0.17 11 14 14
18" tube 3 ft 5.83 0.17 10 13 13
18" tube 4 ft 7.78 0.22 13 18 18
24" tube 3 ft 10.37 0.29 18 24 24
24" tube 4 ft 13.82 0.39 24 31 31

Pouring in Canada? Footings have to reach below the frost line, and that depth changes a lot between provinces, and so does the tube size your municipality will accept. Work out the depth first, then come back and price the concrete.

Bags per cubic yard and cubic metre

Bags needed to fill one cubic yard and one cubic metre
Bag Yield (cu ft) Per cubic yard Per cubic metre Per pallet Sold in
40 lb 0.3 90 118 80 US
50 lb 0.375 72 94 n/a US
60 lb 0.45 60 78 56 Both
80 lb 0.6 45 59 42 Both
25 kg 0.374 72 94 n/a Canada
30 kg 0.449 60 79 n/a Canada

Yields are the typical figures printed on standard ready-mix bags. Pallet counts are typical retail quantities and vary by brand, so confirm with your supplier. "n/a" means we could not confirm a standard count.

Before you pour

  • Order in whole or half yards. Ready-mix suppliers rarely sell odd fractions, and most have a minimum charge.
  • Mixing more than about 25 bags by hand is a long day. Past that, hire a mixer or switch to ready-mix.
  • Compact the base first. Soft spots let the slab sink and crack, and they quietly swallow extra concrete.
  • Rebar and mesh are not in these numbers. Most slabs and structural footings need reinforcement. Check what your local code requires.
  • Have everything ready before the first bag opens. A pour that stops part-way leaves a cold joint, which is a permanent weak line.

These are estimates to help you buy materials. Footing sizes, depths and reinforcement are set by your local building code. Confirm them with your building department or an engineer before you dig.

Common questions

How many bags of concrete are in a cubic yard?
A cubic yard is 27 cubic feet, so it takes 45 bags of 80 lb mix, 60 bags of 60 lb, or 90 bags of 40 lb. Those come from the yields printed on the bags: 0.60, 0.45 and 0.30 cubic feet of mixed concrete each. Always check the bag you are buying, because yields vary a little between brands.
How many bags of concrete are in a cubic metre?
About 79 bags of 30 kg mix, or 59 bags of 80 lb. A cubic metre is roughly 1.31 cubic yards, so it is a noticeably bigger pour than a cubic yard. Worth checking twice if you are ordering in Canada.
How much concrete do I need for a 10x10 slab?
A 10 ft × 10 ft slab at 4 inches thick needs 1.36 cubic yards (1.04 m³) including a 10% waste allowance. That is 62 bags of 80 lb mix. At 6 inches thick it is half again as much. The table above this answer covers the other common slab sizes.
How many bags of concrete are on a pallet or skid?
Typically 42 bags of 80 lb, 56 bags of 60 lb, or 80 bags of 40 lb. A pallet is called a skid in much of Canada. These counts vary by brand and by retailer, so confirm before you plan a truck load. Remember too that a full pallet of 80 lb bags weighs over 3,300 lb.
How much concrete do I need for a 10 inch sonotube?
A 10 inch tube filled to 4 feet takes 2.4 cubic feet (0.07 m³) with 10% waste, which is 4 bags of 80 lb mix per footing. Multiply by the number of footings, which the calculator does for you.
Should I use bags or order ready-mix?
Roughly half a cubic yard is the turning point. Below that, bags are easier and there is no delivery minimum. Above it, you are mixing 25+ bags by hand, and ready-mix is usually cheaper per yard as well as far less work. Most suppliers sell in whole or half yards and have a minimum order, so ask before you book.
How much extra concrete should I order?
Add 5% to 10%. The allowance covers spillage, an over-dug hole, ground that is not perfectly level, and the slab sitting slightly deeper in places. Running out part-way through a pour is far worse than having a little left over, because a cold joint in the middle of a slab is a permanent weak line.
How much concrete do I need for a fence post?
For a 4×4 post in a 12 inch hole dug 3 feet deep, about 2.31 cubic feet per post, because the post itself displaces some of the hole. Switch the calculator to Post holes to work out a whole fence line at once.