Concrete Weight Calculator
Enter your concrete dimensions, choose a shape and mix type, and get the total weight in kilograms, pounds, and tonnes. Results include volume, number of pre-mix bags needed, and an optional cost estimate. Switch between metric and imperial at any time.
How to calculate the weight of concrete
Concrete weight is simply the volume of the pour multiplied by the density of the mix. The standard formula is: Weight = Volume x Density. Normal-weight gravel concrete has a density of about 2,404 kg/m3 (150 lb/ft3), but reinforced concrete runs closer to 2,500 kg/m3 because of the embedded steel. Asphalt concrete is slightly lighter at about 2,243 kg/m3. This calculator handles the volume geometry for you - just pick your shape, enter the dimensions, choose a mix type, and the weight updates instantly. A waste allowance of 5-10% is added to the volume to account for spillage, uneven sub-bases, and slight over-ordering, which is standard practice in the industry.
How to estimate concrete bag quantities
Pre-mix bags of dry concrete are sold in several sizes. Common imperial sizes are 40 lb, 60 lb, and 80 lb, which yield roughly 0.30, 0.45, and 0.60 cubic feet when mixed. Common metric sizes are 25 kg and 40 kg, yielding about 0.012 and 0.019 cubic metres. To find the number of bags needed, divide the total volume (including the waste allowance) by the yield per bag, then round up to the nearest whole bag. For large pours - typically over a cubic yard or 0.75 m3 - it is more economical to order ready-mix concrete by the cubic yard from a batch plant rather than buying individual bags.
Slab, cylinder, and column volume formulas
This calculator supports three common concrete shapes. For a rectangular slab or wall, volume = length x width x thickness. For a round cylinder or circular column, volume = pi x radius2 x height (remember to halve the diameter to get the radius). For a square column, volume = side x side x height. Imperial users should note that slab thickness is entered in inches while length and width are in feet - the calculator automatically converts. When using metric, length and width are in metres and thickness is in centimetres.
Reinforced versus plain concrete - why density matters
The density of plain concrete ranges from about 2,240 to 2,400 kg/m3 depending on aggregate type and mix design. Reinforced concrete, which embeds steel rebar or mesh, has a higher effective density of roughly 2,500 kg/m3 because steel (about 7,850 kg/m3) replaces some of the voids. For structural load calculations, using the correct density matters: underestimating the weight of a concrete beam or slab by even 5% can affect deflection and bearing design. Asphalt concrete uses bitumen as a binder instead of cement paste, giving it a slightly lower density and different compaction behavior.
Concrete type densities
| Concrete type | Density (kg/m³) | Density (lb/ft³) | Typical use |
|---|---|---|---|
| Gravel concrete (normal weight) | 2,404 | 150.0 | Slabs, foundations, general construction |
| Portland cement concrete | 2,300 | 143.6 | Structural slabs, walls |
| Portland-Limestone concrete | 2,371 | 148.0 | Low-carbon structural work |
| Reinforced concrete | 2,500 | 156.1 | Load-bearing columns, beams, bridges |
| Asphalt concrete | 2,243 | 140.0 | Roads, driveways, parking lots |
Standard densities used by this calculator. Values align with ACI 318 and OmniCalculator reference data.
Frequently asked questions
How much does a cubic foot of concrete weigh?
A cubic foot of standard gravel concrete weighs about 150 lb (68 kg). Reinforced concrete is a bit heavier at roughly 156 lb/ft3 (2,500 kg/m3), while asphalt concrete is slightly lighter at about 140 lb/ft3 (2,243 kg/m3). These values assume normal-weight aggregate and a typical water-cement ratio.
How much does a cubic yard of concrete weigh?
One cubic yard of standard gravel concrete weighs about 4,050 lb (1,836 kg), or just over 2 short tons. Reinforced concrete is heavier at approximately 4,215 lb/yd3. A standard ready-mix truck can carry about 10 cubic yards, which equals roughly 40,500 lb - close to the legal weight limit for most highways.
How many bags of concrete do I need for a 10x10 slab at 4 inches thick?
A 10 ft x 10 ft slab at 4 inches (0.33 ft) thick has a volume of about 33.3 cubic feet. Adding a 5% waste allowance brings this to about 35 cubic feet. Using 80 lb bags (0.60 ft3 each), you would need about 59 bags. With 60 lb bags (0.45 ft3 each) you would need about 78 bags. For a pour this size, ready-mix concrete is often more cost-effective.
What is the density of concrete in kg/m3?
Standard gravel concrete has a density of about 2,404 kg/m3. Portland cement concrete is typically 2,300 kg/m3, Portland-Limestone concrete is about 2,371 kg/m3, reinforced concrete runs to around 2,500 kg/m3, and asphalt concrete is approximately 2,243 kg/m3. For high-density shielding concrete (used in nuclear applications), densities can reach 3,500 kg/m3 or more.
Should I add a waste allowance when ordering concrete?
Yes. Industry standard practice is to order 5-10% more concrete than the calculated volume. Waste occurs from spillage during pouring, slightly uneven sub-base surfaces, concrete left in the delivery chute, and rounding up when scheduling truck loads. For simple flat slabs, 5% is usually sufficient. For complex formwork with many corners or curves, use 10-15% to avoid running short mid-pour.
How much does a 4-inch concrete slab weigh per square foot?
A 4-inch thick concrete slab weighs about 50 lb per square foot (244 kg/m2) using standard gravel concrete at 150 lb/ft3. This is calculated as 0.333 ft x 150 lb/ft3 = 50 lb/ft2. For a 6-inch slab the figure rises to 75 lb/ft2 (366 kg/m2). This "dead load" value is needed for structural floor and foundation design.