Concrete Weight Calculator

How do you calculate the weight of concrete?

Concrete weight is volume times density. Work out the volume in cubic feet, then multiply by the weight of one cubic foot of concrete:

Cubic feet = length (ft) × width (ft) × thickness (in) ÷ 12
Weight (lb) = cubic feet × density (lb/ft³)
US tons = pounds ÷ 2,000 · kilograms = pounds ÷ 2.2046

The calculator above does this for any rectangle and gives the result in pounds, US tons, kilograms and cubic yards, plus the weight per square foot of surface. Pick one of three densities:

• 150 lb/ft³: the standard planning figure for normal-weight concrete. Washington State DOT uses 150 lb/ft³ for plain concrete in bridge design.
• 145 lb/ft³: a middle value. FHWA bridge research reports unit weights from about 140 to 155 lb/ft³, rising about 1 lb/ft³ for every 1,000 psi of strength, and the same FHWA page uses 145 lb/ft³ for normal-weight concrete in the AASHTO elastic-modulus (stiffness) provision for strengths up to 5,000 psi.
• 140 lb/ft³: the density QUIKRETE lists on its Concrete Mix (No. 1101) data sheet, a good choice for a pour made from bags.

If your supplier or engineer gives you a measured unit weight, use that instead. The answer only gets as accurate as the density you put in.

How much does a concrete slab weigh? Common sizes

Most people want the weight of a specific slab: to plan removal, check what a trailer can carry, or tell an engineer what a floor will hold. This table gives common slab sizes at 4 in thick, computed with the same formula the tool uses.

For a 6 in slab, multiply every weight by 1.5: a 10 × 10 ft slab at 6 in is 7,500 lb and a 20 × 20 ft slab is 30,000 lb (15 tons). For a 5 in slab, multiply by 1.25.

How much does concrete weigh per square foot?

Each inch of thickness adds about 12.5 lb to every square foot at 150 lb/ft³, because one square foot one inch thick is 1/12 of a cubic foot. That makes per-square-foot weight easy to estimate in your head: thickness in inches × 12.5.

This is the dead load of the concrete itself. Floor coverings, reinforcement and anything placed on the slab add to it. Whether a deck, roof or upper floor can carry that load is a question for a structural engineer and your local building department, not for a weight calculator.

How much does a cubic foot, cubic yard and cubic meter of concrete weigh?

A cubic foot of normal-weight concrete weighs about 140–150 lb. Bigger units follow directly: a cubic yard is 27 ft³, and a cubic metre is 35.31 ft³.

To go from volume to weight for a whole pour, multiply the cubic yards by the per-yard figure. If you still need the volume, size it first with the concrete yards calculator, then come back here.

What changes the weight of concrete?

The aggregate does most of the work. Stone makes up the bulk of a normal mix, so a denser stone gives a heavier concrete and lightweight aggregate gives a much lighter one. FHWA’s bridge research also found that stronger mixes run slightly heavier, about 1 lb/ft³ per 1,000 psi of compressive strength. Entrained air makes concrete lighter, and steel makes it heavier: WSDOT adds 5 lb/ft³ for reinforced concrete, using 155 lb/ft³ for dead load. This calculator covers normal-weight concrete; for lightweight structural concrete, use the unit weight on your mix design.

Weight of other concrete shapes

The same rule, volume × density, works for any shape. These common objects were computed at 150 lb/ft³:

• Concrete steps: three steps 4 ft wide with 7 in risers and 11 in treads hold about 12.83 ft³, about 1,925 lb.
• Wall: a wall 20 ft long, 4 ft high and 8 in thick is 53.33 ft³, about 8,000 lb or 4 tons.
• Countertop: an 8 × 2 ft top 1.5 in thick weighs about 300 lb.
• Post footing: a 10 in round hole 3 ft deep filled with concrete weighs about 245 lb at 150 lb/ft³, or 229 lb at 140.
• Pier: a 12 in diameter column 4 ft tall is 3.14 ft³, about 471 lb.
• Test cylinder: a 6 × 12 in cylinder weighs about 29.5 lb; a 4 × 8 in cylinder about 8.7 lb.

For a round shape, the volume is 3.1416 × radius² × height, with all three in feet. For steps and walls, the concrete steps calculator and concrete wall calculator give the volume; multiply it by your density. Hollow concrete blocks are not solid, so do not use this calculator for a block wall; block weight depends on the unit, and the concrete block calculator handles block counts.

Concrete weight in metric

Outside the US, concrete is measured in cubic metres and weighed in kilograms or tonnes. At 150 lb/ft³ a cubic metre of concrete is about 2,403 kg; at 140 lb/ft³ it is about 2,243 kg.

To find the weight of a metric slab, multiply length × width × thickness in metres, then multiply by the density in kg/m³. A 5 × 4 m slab 100 mm thick is 5 × 4 × 0.1 = 2 m³, which weighs about 4,806 kg (4.81 tonnes) at the higher figure and about 4,485 kg (4.49 tonnes) at the lower one. Per square metre, a 100 mm slab weighs roughly 224–240 kg (0.1 m × 2,243–2,403 kg/m³). The kg/m² column above is for whole inches at 150 lb/ft³, so 4 in (101.6 mm) shows 244 kg.

Does wet concrete weigh more than cured concrete?

Fresh concrete includes all its mixing water, and some of that water leaves as the concrete dries, so hardened concrete ends up a little lighter. How much depends on the mix and the drying conditions, and we have not found a single authoritative figure that applies to every slab, so this calculator does not apply a drying adjustment. The 140–150 lb/ft³ range is wide enough to cover typical fresh and hardened normal-weight concrete for planning.

What the data sheet does give is the bagged-mix numbers. QUIKRETE says an 80 lb bag of Concrete Mix takes about 6 pints of water, which is about 6.3 lb, and yields about 0.60 ft³. At the 140 lb/ft³ it lists, 0.60 ft³ of concrete weighs 84 lb, so one mixed bag is roughly 84–86 lb of wet concrete. Field crews check fresh concrete with a unit-weight test on the actual load; when a project needs an exact figure, that test result is the number to use.

Common mistakes when calculating concrete weight

Most weight errors come from mixing units, not from the density. These are the ones that cost the most:

• Entering thickness in feet instead of inches. A 10 × 10 ft slab 4 in thick weighs about 5,000 lb. Enter 4 ft by mistake and you get 60,000 lb, twelve times too much.
• Multiplying cubic yards by the per-cubic-foot density. 1.23 yd³ × 150 gives 185 lb. The right answer is 1.23 yd³ × 4,050 lb, about 5,000 lb. Convert yards to cubic feet first (× 27).
• Mixing up US tons and metric tonnes. 20,000 lb is 10 US tons but only 9.07 tonnes. Haulers and scales in the US usually work in short tons of 2,000 lb.
• Using the wrong density. On a 20 × 20 ft slab 4 in thick, 150 lb/ft³ gives 20,000 lb and 145 lb/ft³ gives 19,333 lb. That 667 lb gap can matter for a trailer near its limit. When it does, use the higher figure or ask your supplier for theirs.
• Forgetting reinforcement and thickened edges. Steel adds weight (WSDOT adds 5 lb/ft³) and a turned-down edge adds volume. Measure the edges as a separate strip and add them.
• Treating weight as load capacity. Knowing a slab weighs 50 lb/ft² does not tell you whether the ground or structure under it can carry it. That needs an engineer and local code.

Concrete weight calculator vs yards, slab and tons calculators: which one to use

This page turns dimensions into weight. Use a different tool when your question is about how much to order or buy:

• Concrete slab calculator: how many cubic yards or bags a slab needs, with waste.
• Concrete yards calculator: volume for any pour when you need to order ready-mix.
• Concrete bag calculator: how many 40, 50, 60, 80 or 90 lb bags fill a given volume.
• Tons to cubic yards: converting gravel, sand and other aggregates between tons and yards; concrete itself is covered on this page.
• Cubic yard calculator: plain volume in yd³ for any material.

Where the densities come from

The three density options are tied to named sources. FHWA report FHWA-HRT-05-057, which compiled data from high-performance concrete bridge projects, states that unit weights range from about 140 to 155 lb/ft³. Washington State DOT’s bridge design memo sets 150 lb/ft³ for plain normal-weight concrete and 155 lb/ft³ for reinforced concrete dead load. QUIKRETE’s Concrete Mix (No. 1101) data sheet lists a density of about 140 lb/ft³ (2,242.5 kg/m³) and a yield of about 0.60 ft³ per 80 lb bag. Brand names on this page are used only to identify the data sheets; this site is independent and not affiliated with any manufacturer.