How this instrument works
Concrete weight is volume multiplied by density, the same basic relationship as any material weight calculation. For a slab or footing, volume is length times width times thickness — with thickness typically given in inches while the footprint is measured in feet, so a unit conversion happens before the multiplication.
Normal-weight concrete (the standard type used in most residential and commercial slabs, footings, and foundations) has a density commonly cited around 150 lb per cubic foot, a figure widely used as the standard reference value in US structural engineering, including in ACI 318 code calculations, though real mix densities typically range from about 145 to 150 lb/ft³ depending on the specific aggregate and mix design. Lightweight structural concrete, which uses different aggregates, runs meaningfully lower and would need a different density entered.
This calculator reports weight in both pounds and US tons, since pounds is more useful for structural load calculations while tons is the more practical unit for trucking, disposal, or crane-lift planning on larger pours.
- Enter the slab or footing's length and width in feet.
- Enter the thickness in inches.
- Leave the density at the standard 150 lb/ft³ default, or enter your specific mix's actual density if known (lightweight concrete especially).
- Read the resulting weight in both pounds and US tons.
A 10 x 10 ft slab, 6 inches thick
A 10 ft by 10 ft patio slab is poured 6 inches (0.5 ft) thick using standard normal-weight concrete. Volume = 10 x 10 x 0.5 = 50 cubic feet. At the standard 150 lb/ft³ density: 50 x 150 = 7,500 lb, or 7,500/2,000 = 3.75 tons — useful for planning how the slab's weight will bear on the soil beneath it or estimating demolition disposal weight down the road.
A larger 20 x 20 ft, 4 in driveway slab scales up: volume = 20 x 20 x (4/12) = 133.333 cubic feet, weight = 133.333 x 150 = 20,000 lb, exactly 10.0 tons — over 2.5 times the first slab's weight despite being only 4 times the area and two-thirds the thickness, since both length dimensions doubling compounds the area increase.
Questions
Is 150 lb/ft³ the exact density of my specific concrete mix?
Probably close, but not exact. 150 lb/ft³ is the standard reference value used in US structural engineering and ACI code calculations, but real normal-weight mixes commonly range from about 145 to 150 lb/ft³ depending on the aggregate type and mix design. For a precise weight estimate on a specific project, use your mix design's actual tested density if it's available.
What density should I use for lightweight concrete?
Lightweight structural concrete uses different aggregates and typically runs meaningfully lower than 150 lb/ft³ — often in the range of 90-120 lb/ft³ depending on the specific lightweight aggregate used. Check your mix design's specified density and enter that instead of the normal-weight default.
Why does the calculator report both pounds and tons?
Pounds is the more useful unit for structural load calculations (like checking soil bearing pressure or joist load capacity), while tons is more practical for planning truck hauling, disposal fees, or crane-lift capacity on larger precast or removed sections — having both saves converting by hand.
Does this weight include rebar or wire mesh reinforcement?
No, this calculates plain concrete weight only, based on the entered dimensions and density. Reinforcement adds relatively little to the total weight of a typical slab and is normally negligible for planning purposes, but it isn't included in this figure.