FREE CONCRETE CALCULATOR
Concrete slab calculator — cubic yards, bags, and rebar in one pass.
Enter the slab dimensions and get ready-mix yardage with waste, premix bag counts, and a rebar grid estimate you can take straight to the supplier. Free, no signup.
Slab inputs
| Volume (no waste) | – |
| Order quantity (with waste) | – |
| 80 lb premix bags | – |
| 60 lb premix bags | – |
| Rebar — total linear feet | – |
| Rebar — 20 ft sticks | – |
| Wire mesh alternative | – |
Estimates only. Verify dimensions, subgrade, waste, and code requirements before ordering. Bags per yard: 45 × 80 lb or 60 × 60 lb.
How the concrete math works
Concrete is ordered in cubic yards: length × width × thickness (in feet) ÷ 27. A 4-inch slab converts thickness as 4 ÷ 12 = 0.333 ft. Waste covers spillage, uneven subgrade, and form deflection — 10 percent is the working default for flatwork, and short-load fees usually make it cheaper to order a quarter-yard heavy than to come up half a yard short with a finishing crew on the clock.
Bags or ready-mix?
Under about half a yard, bags make sense. At a full yard you are mixing 45 eighty-pound bags — nearly two tons through a wheelbarrow — and ready-mix with a short-load fee almost always wins on labor alone. The calculator shows both so you can price the crossover for your job.
Yardage is step one. Pricing the whole job is the hard part.
FieldSquire turns a walkthrough — voice notes, photos, measurements — into an editable, line-item estimate with your own labor rates and markup, then sends a branded PDF for signature. Solo plan free for 14 days, no credit card.
Start the free Solo trialFrequently asked questions
How many cubic yards of concrete do I need for a 24x24 slab?
A 24 by 24 foot slab at 4 inches thick needs about 7.1 cubic yards before waste. At 10 percent waste, order roughly 7.9 yards — most contractors round up to 8. Use the calculator above to adjust thickness and waste for your job.
How thick should a concrete slab be for a driveway?
Residential driveways are commonly 4 inches for cars and 5 to 6 inches where trucks or RVs will park. Check local code and soil conditions; thicker edges and reinforcement matter as much as nominal thickness.
How many 80 lb bags of concrete make a yard?
About 45 bags of 80 lb premix make one cubic yard. For 60 lb bags it takes about 60. Past roughly one yard, ready-mix delivery is usually cheaper and far less work than bags.
How much rebar do I need in a slab?
A common residential grid is #3 or #4 bar at 18 inches on center each way, held at mid-depth on chairs. The calculator estimates total linear feet and 20-foot stick counts from your spacing; verify with local code for structural slabs.
Does this calculator include the price of concrete?
No — material prices vary by region and supplier. It returns quantities. To turn quantities into a priced, line-item bid with your local rates, try the FieldSquire estimating app free for 14 days.