Concrete Calculator
Work out exactly how much concrete your project needs — in cubic yards, bags, and dollars — for slabs, footings, columns, and stairs.
Results are estimates for planning only. Concrete volume can vary with subgrade, formwork, and finishing. Always order a 5–10% overage and confirm against your supplier's quote and local building code.
Quick Reference — Common Slab Sizes
Looking for a fast answer? These are the volumes for the most common slab dimensions, before waste. The calculator above handles any size, plus footings, columns, and stairs.
| Slab size | Floor area | 4" thick | 6" thick | 80 lb bags (4") |
|---|---|---|---|---|
| 8 × 8 ft | 64 sq ft | 0.79 cu yd | 1.19 cu yd | 36 |
| 10 × 10 ft | 100 sq ft | 1.23 cu yd | 1.85 cu yd | 56 |
| 10 × 12 ft | 120 sq ft | 1.48 cu yd | 2.22 cu yd | 67 |
| 12 × 12 ft | 144 sq ft | 1.78 cu yd | 2.67 cu yd | 80 |
| 12 × 16 ft | 192 sq ft | 2.37 cu yd | 3.56 cu yd | 107 |
| 16 × 16 ft | 256 sq ft | 3.16 cu yd | 4.74 cu yd | 143 |
| 20 × 20 ft | 400 sq ft | 4.94 cu yd | 7.41 cu yd | 223 |
| 24 × 24 ft | 576 sq ft | 7.11 cu yd | 10.67 cu yd | 320 |
| 30 × 30 ft | 900 sq ft | 11.11 cu yd | 16.67 cu yd | 500 |
For driveways and any slab carrying vehicle weight, use 5–6 inches thick. Patios, walkways and shed pads are typically 4 inches.
How to Measure for Concrete
Accurate measurements are the difference between one clean pour and an awkward second delivery. Measure to the inside face of your forms, and keep length and width in feet but depth or thickness in inches — the calculator handles the conversion.
Slabs & patios
Measure the length and width of the formed area in feet. For thickness, use the finished depth of concrete: 4" for patios and walkways, 5–6" for driveways. If the slab is L-shaped, split it into rectangles and add the results.
Footings
Enter the total trench length in feet, then the footing width and depth in inches. For a continuous footing around a building, use the full perimeter length.
Round columns & piers
Measure the tube or form diameter in inches and the pour height in feet. Set the quantity to pour several identical columns at once.
Stairs
Count the steps, then measure the rise (height of one step) and run (tread depth) in inches, plus the stair width in feet. The calculator treats the steps as solid concrete.
Worked Example — Pouring a 12 × 16 ft Patio
Numbers help these formulas make sense. Here's how to think through a typical backyard patio, end to end.
Project: a 12 ft × 16 ft rectangular concrete patio, finished 4 inches thick, on a compacted gravel base.
- Volume in cubic feet = 12 × 16 × (4 ÷ 12) = 64 cu ft
- Volume in cubic yards = 64 ÷ 27 = 2.37 cu yd
- Add 10% waste for spillage and uneven subgrade → 2.37 × 1.10 = 2.61 cu yd
- Round up to a clean order → 2.75 cu yd (suppliers usually deliver in 0.25 cu yd increments)
- Ready-mix cost at $150/cu yd = $150 × 2.75 ≈ $413, plus delivery and any short-load surcharge.
- Or bagged alternative: 64 cu ft × 1.10 ÷ 0.60 cu ft per 80 lb bag ≈ 118 bags at ~$6 each ≈ $708 in materials — and you have to mix every bag by hand. Ready-mix wins clearly at this size.
- Don't forget the base: a typical 4-inch compacted gravel base under the patio is about 1.6 cu yd of gravel. Work that out with the gravel calculator.
Smaller example — a 10 × 10 shed pad
A 10 × 10 ft slab at 4 inches works out to 1.23 cu yd of concrete, or 1.4 cu yd with 10% waste. That sits right at the crossover where bags still make sense (~62 of the 80 lb bags at roughly $370). A short-load ready-mix delivery — typically a $90–$150 surcharge on top of the per-yard cost — saves the labor of mixing 62 bags by hand. Most DIYers go ready-mix at 1 cu yd and above.
Concrete Prices in 2026 — A Practical Guide
Concrete is sold two ways: as bagged pre-mix you mix yourself, or as ready-mix delivered by truck. Prices vary by region — Northeast and West Coast metros sit at the high end, rural South and Midwest at the low end. The figures below are typical 2026 US ranges; always confirm with two or three local suppliers before a big pour.
Ready-mix concrete (delivered)
- Per cubic yard: roughly $130 – $170 for a standard 3,000–4,000 PSI mix in 2026.
- Delivery fee: $90 – $150 minimum, sometimes folded into the per-yard price.
- Short-load surcharge: $50 – $150 on orders under about 8–10 cu yd — the truck still has to come out for a small pour.
- Wait-time charge: usually free for the first 5–7 minutes per yard, then $1 – $2 per minute. Have your forms and crew ready before the truck arrives.
Bagged pre-mix concrete
- 80 lb bag: about $5 – $7 each. Yields ~0.60 cu ft. 45 bags per cubic yard.
- 60 lb bag: about $4 – $6 each. Yields ~0.45 cu ft. 60 bags per cubic yard.
- 40 lb bag: about $3 – $5 each. Yields ~0.30 cu ft. 90 bags per cubic yard.
When to choose which
The crossover point is around 1 cubic yard. Below that, bags are simpler — you don't have to schedule a truck or worry about a short-load surcharge. Above it, ready-mix is both cheaper per yard and dramatically less labor. For a 2+ cu yd pour with bags, you're mixing 90+ bags by hand or with a small mixer — a long, hard day.
One in-between option for 1–3 cu yd projects: some suppliers offer small-batch trailers you tow yourself, with the mix added on demand. Costs sit between bagged and full ready-mix and you avoid both the short-load fee and the hand mixing.
Common Mistakes to Avoid
- Forgetting the waste allowance. Subgrade is never perfectly level. Skipping the 5–10% overage is the number one reason pours run short.
- Mixing up feet and inches for thickness. Entering "4" as feet instead of inches overestimates volume 12×. Thickness is in inches.
- Measuring outside the forms. Concrete fills the space inside the formwork — measure there, not the outer edge of the lumber.
- Buying bags for a big pour. Anything over ~1 cubic yard is cheaper and far easier as truck-delivered ready-mix.
- Ignoring slope and over-dig. Trenches and footings are almost always slightly deeper than planned — round up, never down.
- Skipping the gravel base. Pouring concrete directly on dirt invites frost heave and cracking. Plan a 4-inch compacted gravel base — estimate it with the gravel calculator.
Frequently Asked Questions
A 10 ft × 10 ft slab poured 4 inches thick is 33.3 cubic feet, or about 1.23 cubic yards. Add 10% waste and you should order roughly 1.4 cubic yards of ready-mix concrete.
An 80 lb bag of pre-mix concrete yields about 0.60 cubic feet. A cubic yard is 27 cubic feet, so you need about 45 bags of 80 lb concrete per cubic yard (60 bags of 60 lb, or 90 bags of 40 lb).
Yes. Always add a 5–10% waste allowance for spillage, uneven subgrade, and over-excavation. Running short mid-pour creates a cold joint or a costly second delivery, so ordering slightly extra is cheap insurance.
Four inches is standard for patios, walkways, and shed floors. Use 5–6 inches for driveways or anything that carries vehicle weight. Always confirm with your local building code.
Bagged pre-mix suits small jobs under about half a cubic yard. Beyond roughly 1 cubic yard, ready-mix delivered by truck is usually cheaper and far less labor than mixing dozens of bags by hand.
Typical 2026 US ranges are $130–$170 per cubic yard for a standard mix, plus a $90–$150 delivery minimum and a short-load surcharge of $50–$150 on orders under about 8–10 cu yd. Prices vary by region — get two or three local quotes for any pour over 1 cubic yard.
Most suppliers deliver as little as 1 cubic yard, but anything under their full-truck threshold (often 8–10 cu yd) carries a short-load surcharge. For fractions of a yard, look into a tow-yourself trailer service or stick with bagged pre-mix.
Fresh concrete sets enough to walk on in 24–48 hours. Vehicles should stay off for at least 7 days. Full design strength is reached at about 28 days, though concrete keeps gaining strength slowly for years after that.
For thin patios and walkways at 3–4 inches, fiber-reinforced mix or welded wire mesh is usually enough to control cracking. Driveways and any slab carrying vehicles or structural loads need rebar — typically #4 rebar on a 16–24 inch grid. Always check local code.
About 4,050 lb — roughly 2 tons — for a standard mix. That works out to 150 lb per cubic foot, useful when checking whether your subgrade and forms can handle the load before the pour.
Cement is the gray powder that binds everything together — usually Portland cement. Concrete is the finished material: cement mixed with aggregate (sand and gravel) and water. Asking for "cement" when you mean concrete is the trade equivalent of asking for "flour" when you want bread.
Yes, almost always. A 4-inch layer of compacted gravel gives the slab a stable base, drains water away, and reduces cracking from frost heave. Size the base layer with the gravel calculator.