Fast slab weight estimates for concrete and lightweight mixes. Set units, openings, thickness, density, and rebar allowance. Add wastage, multiply slabs, and plan deliveries.
| Case | Shape | Size | Thickness | Density | Openings | Rebar | Slabs | Wastage |
|---|---|---|---|---|---|---|---|---|
| A | Rectangular | 6 m × 4 m | 150 mm | 2400 kg/m³ | 0 m² | 12 kg/m² | 1 | 3% |
| B | Rectangular | 10 ft × 12 ft | 6 in | 1850 kg/m³ | 8 ft² | 0 kg/m² | 4 | 5% |
| C | Circular | Diameter 5 m | 120 mm | 2500 kg/m³ | 0.5 m² | 15 kg/m² | 2 | 2% |
Use the table to test entries and compare scenarios.
Where ρ is density, t thickness, Aₒ openings area, aᵣ rebar allowance, and w wastage percent.
Slab self weight is a major contributor to dead load in building design. It influences column sizing, foundation demand, lifting plans, and trucking quantities. This calculator estimates slab mass and weight from geometry, thickness, and material density, then adjusts the result for openings, reinforcement allowance, quantity, and wastage. It supports rectangular floor plates and circular pads, and it reports totals in kilograms, tons, pounds, and kilonewtons for coordination across teams.
Begin by selecting the unit system that matches your drawings. Choose the slab shape, then enter thickness with care; area is multiplied by thickness, so small thickness changes create large volume changes. Provide length and width for rectangles, or diameter for circles. Next, subtract major voids by entering an openings area. Typical openings include stair cores, elevator shafts, and large service trenches. The calculator converts entries to a consistent metric basis, computes gross area, net area, volume, and concrete mass, and then adds optional rebar mass and wastage.
Select a density preset that matches the specified mix, or choose custom density when you have project data. Normal concrete is often near 2400 kg per cubic meter, lightweight mixes can be lower, and high density mixes can be higher. If you want a preliminary allowance for reinforcement, enable the reinforcement option and enter rebar mass per square meter. This is practical when bar schedules are incomplete but you still need an order of magnitude check for handling, crane capacity, or dead load summaries. Finally, set slab count and a contingency percentage to reflect site realities and procurement rounding.
Example data: a 6 m by 4 m slab, 150 mm thick, density 2400 kg per cubic meter, no openings, rebar allowance 12 kg per square meter, one slab, and 3 percent wastage. Gross and net area are 24.0 square meters. Thickness is 0.150 m, so volume is 24.0 times 0.150 equals 3.600 cubic meters. Concrete mass is 3.600 times 2400 equals 8640 kg. Rebar mass is 12 times 24.0 equals 288 kg. Subtotal per slab is 8928 kg. With 3 percent wastage, total mass becomes about 9196 kg, and total weight is about 90.18 kN.
Use outputs to compare options: reducing thickness, increasing openings, or switching to lightweight mixes can cut dead load quickly. Always confirm density, thickness tolerances, and opening quantities from the latest drawings and specifications. For critical work, verify results with structural engineer and supplier before committing to pours.
Use the value specified in your mix design or project specifications. If unknown, start with 2400 kg/m³ for normal concrete, then refine using supplier data, test reports, or lightweight and high-density presets as appropriate.
Include it when you need a closer handling or dead load estimate and bar schedules are uncertain. Enter an allowance in kg/m² from typical detailing or prior projects. Turn it off for pure concrete volume and mass checks.
Sum the plan areas of major voids such as shafts, stair openings, and large trenches. Use drawing dimensions and include only openings that pass through the slab thickness; small sleeves usually have negligible effect.
Differences come from moisture content, actual density, thickness tolerances, formwork camber, and rounding of deliveries. Reinforcement and embedded items may also vary. Treat allowances as estimates and validate with updated drawings and supplier tickets.
Many teams use 2–5% for concrete handling and trimming, but it depends on access, pumping distance, and finishing method. Increase wastage for complex geometry, tight pours, or when multiple small pours cause more leftovers.
Yes, select Custom density and enter the material density in kg/m³. Ensure thickness and units are correct, and remember the rebar allowance assumes steel reinforcement; set it to zero for unreinforced materials.
Divide total mass by net area to get kg/m², then multiply by 9.80665 to convert to N/m². For kN/m², divide by 1000. Use net area so openings are already excluded.
Measure accurately, choose density, and verify before pouring always.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.