Concrete Weight Calculator
A {length}×{width} ft slab poured {thickness} in thick weighs about {pounds} lb, or {tons} tons.
Weight for common slab sizes
| Slab size | Cubic feet | Weight | Tons |
|---|---|---|---|
| 4×4 ft, 4 in | 5.3 | 800 lb | 0.40 |
| 6×6 ft, 4 in | 12.0 | 1,800 lb | 0.90 |
| 10×10 ft, 4 in | 33.3 | 5,000 lb | 2.50 |
| 12×12 ft, 4 in | 48.0 | 7,200 lb | 3.60 |
| 20×20 ft, 4 in | 133.3 | 20,000 lb | 10.00 |
| 10×10 ft, 6 in | 50.0 | 7,500 lb | 3.75 |
| 24×24 ft, 5 in | 240.0 | 36,000 lb | 18.00 |
Plain unreinforced concrete at 150 lb per cubic foot. No waste allowance — this is the weight of the finished, placed slab, not the volume purchased.
How the math works
Concrete's weight is a straightforward density calculation once you have the volume: multiply cubic feet by the typical placed density of concrete.
pounds = cubic feet × 150
tons = pounds ÷ 2000
150 lb per cubic foot is a standard figure for normal-weight concrete without significant aggregate substitution. Lightweight concrete mixes, sometimes used in specialty applications, weigh less; this calculator assumes standard mix.
Wet vs. cured — a smaller difference than people expect
Fresh concrete contains all its mix water, including water that will later be consumed by hydration or simply evaporate. Cured concrete weighs slightly less, since some water leaves as it dries — but the difference is modest, not dramatic. The distinction that actually matters isn't weight, it's behavior: fresh concrete is a fluid and pushes sideways on formwork with real pressure that depends on placement rate and temperature, while cured concrete pushes on nothing. A form blowout on a wall pour is a fresh-concrete pressure failure, not a weight problem — that's the more useful way to think about "wet vs. cured" than the small mass difference.
Steel runs around 490 lb per cubic foot, roughly 3.3 times the density of concrete, but rebar occupies a small enough fraction of a typical slab's volume that even heavy residential reinforcement only adds a modest percentage to the total weight. Where it matters enormously is demolition: unreinforced concrete breaks into separate pieces, while reinforced concrete breaks and then stays connected — every piece is tied to its neighbors by steel that has to be cut, not just broken. That means more labor, different equipment, and slower loading, since the debris won't separate cleanly. Many disposal facilities also price and handle rebar-laden concrete differently, and some require the steel separated out for recycling.
When you're getting a demolition quote, tell the contractor whether the slab is reinforced and how heavily — the weight tells them the tonnage, but the reinforcement tells them the hours.
A 20×20 ft patio at 4 inches thick: 400 sq ft × (4 ÷ 12) ft = 133 cubic feet, or about 4.9 cubic yards. At roughly 4,000 lb per cubic yard, that's close to 19,700 lb — nearly 10 tons. Almost nobody picturing a patio demolition arrives at ten tons on their own, and that number is what actually determines the container size, the equipment, and the disposal cost — whether it's a weekend DIY project at all.
Before you buy
- For structural or load calculations, use an engineer's figure for your specific mix and reinforcement rather than this planning estimate.
- If you're figuring out how much concrete to buy rather than how much a finished slab weighs, use the slab calculator instead — it accounts for waste and gives bags or cubic yards.
- Demolition and disposal of broken concrete is typically priced by weight — this calculator gives a starting estimate for how much a slab you're removing weighs.
Common questions
How much does a slab of concrete weigh?
About 150 lb per cubic foot of placed concrete. A 10×10 ft slab 4 inches thick weighs roughly 5,000 lb, or 2.5 tons.
Why does weight matter for a slab or a load?
Weight matters for structural design — what a floor, trailer, or lift needs to support — and for hauling broken concrete, since disposal and trucking are usually priced or limited by weight, not volume.
Does reinforced concrete weigh more?
Slightly. Rebar and wire mesh add a small amount of weight on top of the plain concrete figure here — typically a few percent for standard residential reinforcement, not enough to change ballpark planning numbers.
How much does a cubic yard of concrete weigh?
About 4,050 lb, or just over 2 tons, using the standard 150 lb per cubic foot figure and 27 cubic feet per cubic yard.
Does this include the weight of a gravel base?
No, this is concrete only. A gravel base sits under the slab and isn't part of the poured concrete's weight — see the gravel calculator if you need that figure separately.