gizmobench

Concrete Yard Calculator

Ready-mix is batched, delivered and billed in cubic yards, so that is the figure this page leads with. Type the slab in the units you measured it in, feet and inches or metres and millimetres, mixed across the three fields, and read the cubic yards with your waste allowance already in, the volume before waste underneath, and cubic metres and cubic feet beside them. There is no price field, because a rate per cubic yard is set regionally and moves.

12 ft10 ft5 in
To orderincl. 10% waste
Cubic yards2.04yd³1.56 m³ · 55.00 ft³ · 1.85 yd³ before waste
80 lb bags59
Length
Width
Thickness
Waste
Bag size
Lead with

Mix the units freely: a length in feet, a width in metres and a thickness in inches all land in the same volume. The bag count is for the 80 lb bag selected above and rounds up, because half a bag is not something you can buy.

  • 12 ft x 10 ft x 5 inone-car pad, 10% waste
    2.04 yd³ · 1.56 m³ · 59 bags
  • 20 ft x 20 ft x 0.5 ftdouble garage, all in feet, no waste
    7.41 yd³ · 5.66 m³ · 213 bags
  • 3 m x 3 m x 100 mmmetric entry, 5% waste
    1.24 yd³ · 0.95 m³ · 36 bags
Volume, never structure. Exact arithmetic on the dimensions you enter, in the units you enter them, plus the waste you choose. It cannot know your subgrade, your local price of concrete, or what thickness a structure needs. Thickness is a measurement you type and this page reads back to you: it never proposes one, and it prints no rebar size and no mix strength, because choosing those for a load is structural work. There is no price field either, since a rate per cubic yard is set regionally and moves.

Common questions

How many cubic yards of concrete is my slab?
Length times width times thickness, converted into cubic yards, which is what the large figure on this page is. A slab 12 feet by 10 feet by 5 inches is 50 cubic feet, and a cubic yard is 27 cubic feet, so it is 1.85 cubic yards before waste and 2.04 with a 10 percent allowance. Type your own measurements and the figure follows; the thickness field takes inches or millimetres directly, so nothing needs converting first.
How much area does one cubic yard of concrete cover?
A cubic yard is 27 cubic feet, so it covers 81 square feet at 4 inches thick, 64.8 square feet at 5 inches and 54 square feet at 6 inches. You can check any of those here: 9 feet by 9 feet by 4 inches, 8 feet by 8.1 feet by 5 inches and 9 feet by 6 feet by 6 inches all read 1.00 cubic yards before waste, whatever the allowance is set to.
Why does a part yard get ordered as a whole one?
Because a truck batches what you order, not what ends up in your forms. Suppliers commonly take an order in whole or quarter yards and bill what leaves the plant, and many add a charge under a minimum load. This page gives the exact figure, waste included, and leaves the rounding to you: read the number here, then round it up to whatever increment your supplier works in and confirm the minimum with them. No rate is shown on this page, since concrete is priced regionally and the figure would go stale.
How much extra should I order?
The allowance is yours to pick: 0, 5 or 10 percent. It covers what a slab loses to an uneven subgrade, to forms that bow out slightly under the pour and to concrete left in the barrow, none of which the page can see from your measurements. The figure before waste stays on screen next to the ordered figure, so you always know which is which.
Bags or ready-mix?
The page gives you both numbers and no opinion. Alongside the cubic yards it shows the whole bags a pour needs at the 40, 60 or 80 lb yield you select, rounded up: a 10 by 20 foot pad at 4 inches with 10 percent waste is 2.72 cubic yards or 79 bags of 80 lb. Mixing that many bags by hand is a different day's work from a truck arriving, and that part is your call.
Can it tell me how thick the slab needs to be?
No. Thickness is something you type in and this page reports back inside the volume, never something it produces. A thickness chosen for a load is structural, so it belongs with an engineer or your local code, not with a volume calculator. Nothing here prints a thickness, a rebar size or a mix strength.

Exact arithmetic on the dimensions you enter, in the units you enter them, plus the waste you choose. It cannot know your subgrade, your local price of concrete, or what thickness a structure needs.