Concrete Calculator
Find how many cubic yards of concrete, or how many 60 lb and 80 lb bags, your slab, footing, or post hole needs. Enter the dimensions, get the order size.
Cubic yards
1.23yd³
Volume
33.3ft³
60 lb bags
75bags
80 lb bags
56bags
Ready-mix is ordered by the cubic yard, and it's worth adding 5-10% to whatever this shows. Bag counts assume the standard yields of 0.45 ft³ for a 60 lb bag and 0.6 ft³ for an 80 lb bag, rounded up.
How the concrete calculator works
Concrete volume is a box: length × width × thickness. The only thing that trips people up is units. This calculator takes length and width in feet and thickness in inches, converts everything to cubic feet, then divides by 27, because a cubic yard is 27 cubic feet.
Formula: volume (ft³) = length × width × (thickness ÷ 12). Cubic yards = volume ÷ 27.
Bag counts come from dividing that volume by what a single bag yields, about 0.45 ft³ for a 60 lb bag and 0.6 ft³ for an 80-pound bag, per the standard manufacturer spec sheets. We round up, since you can't buy a partial bag.
Pouring something structural that needs reinforcement? Run the same length and width through the Rebar Calculator to get grid spacing and total linear footage.
This calculator sizes the order. It doesn't price it, and it doesn't pick the mix: 3,000 psi is the usual residential baseline, and driveways or garage floors often step up to 4,000 psi, which moves the price more than the volume. For dollars, put the same dimensions into the Concrete Cost Calculator, or the Driveway Cost Calculator if you're still deciding between concrete, asphalt, and gravel.
Frequently asked questions
A 10x10 ft slab at the standard 4-inch thickness takes about 1.23 cubic yards, or roughly 74 bags of 60 lb pre-mix. That is right around the point where ordering ready-mix beats hauling bags. Put your own dimensions in above if the slab is not square.
Above about 1 cubic yard, which is roughly a 9x9 ft slab at 4 inches, ready-mix delivery usually wins on both cost and effort. Below that, mixing bags on site is cheaper and easier to schedule. Check the minimum order either way. Most suppliers will not send a truck for less than a yard, and anything under a full load can pick up short load fees.
Order 5-10% more than the calculated volume. Uneven subgrade, spillage, and forms that bow under load all eat into the total, and none of that shows up in a length times width calculation. Coming up short is the expensive mistake: a ready-mix truck rarely comes back for a quarter yard, and by the time a second one arrives your first pour has started to set.
Yes, more than people expect. Volume scales straight with thickness, so a driveway poured at 6 in instead of 4 in needs 50% more concrete for the same footprint. That is why thickness gets its own input here instead of a fixed default.
More calculators
Concrete Cost Calculator
What a concrete slab or driveway actually costs
Driveway Cost Calculator
Concrete, asphalt and gravel priced side by side
Gravel Calculator
Tons and cubic yards of gravel for any area
Mulch Calculator
Cubic yards and bags of mulch for your beds
Topsoil Calculator
Cubic yards, tons, and bags of topsoil for any area
Cinder Block Calculator
Blocks and mortar bags for a CMU wall build
Retaining Wall Calculator
Blocks, rows, and cap units for your wall build
Asphalt Calculator
Tons and cubic yards of asphalt for your driveway
Rebar Calculator
Grid spacing, linear feet & sticks for a slab
Roof Pitch Calculator
Find your roof's angle, slope factor & percentage grade
Roofing Shingles Calculator
Squares and bundles of shingles needed for any roof