Work out concrete volume in cubic yards and the number of 60 lb or 80 lb bags you need.
Quick answer: Concrete is ordered by the cubic yard, and one cubic yard equals 27 cubic feet. A 10 ft × 10 ft slab at 4 in thick is 100 sq ft × 0.33 ft = about 1.23 cubic yards, which is roughly 56 bags of 80 lb mix or 74 bags of 60 lb mix. Bag yields vary by brand, so check the bag.
What are you pouring?
ft
ft
in
4 in suits patios and shed floors; 5–6 in for driveways carrying vehicles.
Concrete needed
2.47 cu yd
66.7 cu ft · 1.89 m³
Order this
2.75 cu yd
Rounded up with 5% waste — ready-mix is sold in 1/4 yd steps
Bag equivalent
80 lb bags (0.60 cu ft each)112 bags
60 lb bags (0.45 cu ft each)149 bags
Weight of the pour4.9 tons (about 4,000 lb per cu yd)
Ready-mix trucks usually carry 8–10 cu yd. A short load under the minimum often carries a fee, and some suppliers charge for the return of unused concrete — say yes to 5% extra rather than a second trip.
Concrete is ordered in cubic yards and almost always rounded up. Add 5–10% for spillage, uneven subgrade and washout. Bag counts assume 80 lb bags at 0.60 cu ft each.
Core facts
One cubic yard
27 cubic feet
80 lb bag yields
about 0.6 cu ft
60 lb bag yields
about 0.45 cu ft
Order extra
5–10% for waste and spillage
What is Concrete Calculator?
Concrete is sold by volume, not by weight, so every project starts with the same question: how many cubic feet does this shape hold? Multiply length by width by thickness in feet and you have cubic feet; divide by 27 and you have cubic yards, which is what a ready-mix truck delivers. For small pours bags are usually simpler. An 80 lb bag of mixed concrete yields roughly 0.6 cubic feet and a 60 lb bag about 0.45 cubic feet, so a full yard works out to about 45 bags of the larger size. That is roughly the point where delivery starts to make more sense than bagging it yourself. Enter your dimensions below and the calculator returns both figures.
Common uses for Concrete Calculator
Estimate a small patio slab before deciding between bags and a delivery
Check how many 80 lb bags a shed floor will take
Compare bagged mix against ready-mix for a medium-sized pour
Order the right amount of concrete without paying for a short load
Size a footing, pad or slab from the same volume formula
Volume first, then how you buy it
Every concrete estimate reduces to one shape: length times width times thickness. The only trick is units. Thickness arrives in inches, so divide by 12 to get feet, then multiply. A 10 by 10 ft slab at 4 in is 100 sq ft times 0.33 ft, which is 33.3 cubic feet, or 1.23 cubic yards. From there, choosing bags or a truck is a price and logistics decision, not a math one.
Bag yields are approximate
The 0.6 cubic feet per 80 lb bag figure is a widely used planning number, not a guarantee. Concrete mixes differ in density, and fast-setting or high-strength products often yield less. Read the yield printed on the bag you are actually buying, then round up. One extra bag costs a few dollars; running short halfway through a slab can ruin the finish.
Weather and timing matter as much as volume
Concrete sets on its own schedule. In hot, windy weather you may have under an hour to place and finish, while in cold weather the mix takes far longer to cure and needs protection from freezing. Order the volume, then plan the people. A pour that is bigger than you can screed and float in time will show every hesitation in the finished surface.
Frequently Asked Questions
How many bags of concrete are in a cubic yard?
About 45 bags of 80 lb mix or 60 bags of 60 lb mix, because a cubic yard is 27 cubic feet and an 80 lb bag yields roughly 0.6 cubic feet. Yields differ between brands and mix types, so check the bag before you buy — a 10 percent shortfall mid-pour is expensive.
Should I order ready-mix or use bags?
Under about one cubic yard, bags are usually cheaper and easier because there is no short-load fee and no delivery window to meet. Above roughly two cubic yards, a truck is faster and often cheaper per yard. In between, weigh the delivery fee, the minimum charge and how fast you can place and finish the concrete.
How thick should a concrete slab be?
Four inches is the common minimum for patios, walkways and shed floors on well-compacted ground. Driveways and slabs that carry vehicles are usually 5 to 6 inches, and any slab over weak or poorly drained subgrade needs more. Local code and your soil decide the final number.
How much extra concrete should I order?
Add 5 to 10 percent for spillage, uneven subgrade and small over-excavation. A pour that runs out mid-slab leaves a cold joint that never bonds properly, and a second delivery usually carries another short-load fee. Extra concrete can always be spread into a pad or a wheelbarrow.
Does the calculator include the subbase?
No. The volume here is the concrete itself. Underneath it you still need a compacted base, typically 4 inches of crushed stone for a slab on grade, plus sand or a vapor barrier where the specification calls for one. Calculate that base separately as gravel.