Concrete Calculator (Yards, Bags & Ready-Mix)
Enter your slab, footing, or column dimensions and get the concrete you need in cubic yards, cubic feet, and 60‑ and 80‑lb bags — plus a recommended overage so you do not come up short mid-pour. The math updates as you type.
Concrete Calculator
Pick a shape, enter dimensions, and read the yardage. A 10% overage is added on the recommended line.
80‑lb bag ≈ 0.60 ft³ yield; 60‑lb bag ≈ 0.45 ft³. For anything over ~1 yd³, ready-mix delivery is usually cheaper and faster than bags. Estimates only — confirm with your supplier.
How much concrete do I need? The formula
Concrete is sold by volume, so every estimate comes down to one thing: cubic feet, converted to cubic yards. The rule is simple — get every measurement into feet, multiply length × width × thickness, then divide by 27 (there are 27 cubic feet in a cubic yard).
| Step | Example: a 20×10 ft slab, 4" thick |
|---|---|
| Thickness to feet | 4 in ÷ 12 = 0.333 ft |
| Volume in cubic feet | 20 × 10 × 0.333 = 66.7 ft³ |
| Cubic yards | 66.7 ÷ 27 = 2.47 yd³ |
| Order with overage | 2.47 × 1.10 = 2.72 yd³ |
Always round up and add 5–10%. Uneven subgrade, spillage, and over-excavation eat concrete fast, and running short mid-pour means a cold joint or an emergency second load. Coming home with a little extra is far cheaper than either.
Contractor Estimate Calculator (Excel & Google Sheets)
Turn quantities into a priced, itemized estimate — materials, labor, markup, and profit, auto-totaled. The estimate you hand the client after the calculator tells you the volume.
Bags or ready-mix?
Bags make sense for small jobs — post holes, a small pad, a repair. Once you pass roughly 1 cubic yard (about 45 × 80‑lb bags), you are mixing all day and paying more per yard than a ready-mix truck would charge. Most suppliers have a short-load minimum and a small short-load fee, so price both once your number climbs. For a driveway or a garage slab, ready-mix is almost always the answer.
Once the pour is priced, send a clean invoice
The calculator gives you the volume; your bid turns it into a price. When the job is done, bill it with an itemized concrete invoice that separates materials, labor, and prep — and quote new work from a concrete estimate template so your margin is in the number before you ever pour.
Frequently asked questions
How many 80-lb bags of concrete are in a cubic yard?
About 45. An 80‑lb bag yields roughly 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 ≈ 45 bags. For 60‑lb bags it is about 60 per yard.
How thick should a concrete slab be?
4 inches is standard for patios, walkways, and residential floors; 5–6 inches for driveways and anything carrying vehicle weight. Thicker pours and load-bearing work should follow local code and, when required, an engineer.
How much extra concrete should I order?
Add 5–10%. Subgrade that is not perfectly level, spillage, and over-dig all consume more than the raw calculation, and running short mid-pour is far more expensive than a little waste.
Is this concrete calculator free?
Yes — free, no sign-up. Enter your dimensions and read the cubic yards, bags, and recommended overage. Numbers are estimates; confirm with your ready-mix supplier before ordering.