Concrete Calculator
This concrete calculator tells you exactly how much concrete to buy for a slab, patio, footing or round column, in cubic yards, cubic feet, and the number of bags of each size.
Enter your dimensions and it updates instantly. It even adds a little extra for waste, so you don't run short in the middle of a pour.
Enter your measurements
Concrete you need
1.23cubic yards
33.3 ft³ · 100 ft² at 4.0" deep
💡 That's 1.23 cubic yards. Around a cubic yard, buying bags gets expensive and heavy, most people switch to ordering ready-mix delivered.
62
80 lb bags
incl. waste
$372
Est. material cost
@ ~$6/bag
- Cubic feet needed
- 33.3 ft³
- Cubic yards needed
- 1.23 yd³
- Order with 10% waste
- 1.36 yd³
- 80 lb bags to buy
- 62
- 60 lb bags to buy
- 82
- 50 lb bags to buy
- 98
- 40 lb bags to buy
- 123
- Ready-mix trucks (10 yd³ each)
- 1
Common examples
| 10 × 10 patio, 4" thick | 1.23 yd³ · 62 × 80 lb bags |
|---|---|
| 12 × 12 slab, 4" thick | 1.78 yd³ · 88 × 80 lb bags |
| 20 ft driveway, 4" thick (10 ft wide) | 2.47 yd³, order ready-mix |
| Single 8" round footing, 3 ft deep | ≈ 2 × 80 lb bags |
The 2-minute guide
Bags vs. ready-mix: where to switch
For small jobs (a few post holes, a shed pad) bagged concrete you mix yourself is cheapest and easiest. But bags add up fast: once you're past about 1 cubic yard (roughly forty-five 80 lb bags) it's usually cheaper and far less work to order ready-mix delivered by the truck.
Why 4 inches is the magic number
Most slabs (patios, walkways, shed floors) are poured 4 inches thick. Thinner slabs crack under weight; thicker ones (5–6 inches) are for driveways and anything a vehicle drives on. Set the depth above to match your project.
Always buy a little extra
The calculator adds a waste margin because real ground is never perfectly flat and some concrete is always lost to spillage and over-excavated spots. Running out mid-pour creates a weak 'cold joint,' so it's normal to keep a bag or two in reserve.
Measure depth in inches, area in feet
Length and width are in feet; depth/thickness is in inches, that's how slabs are described. For a round footing (like a deck post), switch the shape to Circle and enter the tube's diameter.
Frequently asked questions
How many 80 lb bags of concrete are in a cubic yard?
About 45. Each 80 lb bag of standard concrete mix yields roughly 0.6 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 ≈ 45 bags. Sixty-pound bags yield about 0.45 ft³, so you'd need around 60 of those.
How much concrete do I need for a 10x10 slab?
A 10 ft × 10 ft slab at 4 inches thick is about 1.23 cubic yards (33 cubic feet). That's roughly sixty-two 80 lb bags, enough that ordering ready-mix is worth pricing out.
How thick should a concrete slab be?
Four inches is standard for patios, walkways and shed floors. Use 5–6 inches for driveways or anywhere vehicles park. Below about 3.5 inches, slabs crack easily.
Should I buy extra concrete?
Yes, plan for about 10% extra. Ground is rarely perfectly level, and some mix is always lost to spillage. Running short mid-pour creates a weak seam, so a bag or two in reserve is normal.