Slab Calculator
By CalculatorBolt Team | Jan 15, 2025
Calculate concrete slab volume, weight, and rebar needed. Enter slab dimensions, thickness, waste factor, and rebar spacing.
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Calculate Concrete Slab
Typical: 5-10%
Typical: 150 lb/ft³ (2400 kg/m³)
How it Works
Volume = Length × Width × Thickness. We calculate volume, apply a waste factor, and estimate concrete weight. If rebar is included, we calculate the number of bars and total length/weight based on spacing and layout.
Inputs Explained
- Slab Dimensions: Length, width, thickness, and units.
- Waste Factor: Add 5-10% for over-ordering and spillage.
- Rebar: Optional. Include spacing, diameter (#3, #4, #5), layout (grid or one direction), and edge offset.
Example
Slab 20×10×4 in (20×10×0.33 ft):
- Volume = 66 ft³
- Adjusted (5% waste) = 69.3 ft³
- 2.57 cu yd
- Concrete Weight ≈ 5.2 tons (150 lb/ft³)
- Rebar: #4, 12 in spacing, grid, edge 3 in → ~200 ft, ~134 lbs
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Tips & Notes
- Add a waste factor (5–10%) for over‑ordering and spillage.
- Rebar spacing and size depend on engineering requirements and local codes.
- Concrete density varies; use a supplier's value for accurate weight estimates.
FAQs
Number of bars = (Dimension / Spacing) + 1. Total length = sum of bars × dimension, minus edge offsets. The calculator does this automatically.
Around 150 lb/ft³ (2400 kg/m³). Adjust based on your mix design.
It supports both. Choose your units for inputs and outputs.
⚠️ Disclaimer
Informational estimate only. Concrete mix design, rebar spacing, and densities vary by code and supplier. Consult engineers and suppliers for accurate estimates.