Accurately calculate rebar grid count, total length, total weight, and material cost for concrete slabs. Supports metric/imperial switching, lap splice calculation, and SVG layout visualization. No data sent to any server — completely free.
FAQ
How does the rebar calculator work?
Enter your slab length and width, select a rebar size and spacing, set the edge clearance, and click Calculate. The tool returns the number of bars in each direction, total length, total weight, and estimated cost. It also supports lap splice calculations and unit switching.
What is typical rebar spacing?
Common rebar spacing for slabs is 12 inches, 16 inches, or 24 inches on center. For a 4–6 inch thick slab, 16-inch spacing is typical. Always follow your structural engineer's specifications.
How is lap splice length determined?
Lap splice length is typically 40 times the bar diameter (40d). For a #5 bar (5/8-inch diameter), the lap would be about 25 inches. The exact value depends on concrete strength, bar grade, and building code requirements.
How accurate are the results?
The calculator uses standard engineering formulas to produce theoretical estimates. Actual material usage should account for waste, bending, hooks, and overlaps. We recommend adding 5–10% extra. For critical structures, always rely on a licensed structural engineer's calculations.
How to Use the Rebar Calculator
- Enter slab dimensions
Input the length, width, and thickness of your concrete slab. Switch between metric and imperial units as needed. - Select rebar size and spacing
Choose a rebar diameter (U.S. standard #3–#11 or metric 6–32 mm), then set the on-center spacing and edge clearance. - Set lap splice and cost parameters
Enter the lap splice length (defaults to 40× diameter), rebar price per ton, and choose single or double-layer grid. - Review the results
Click Calculate to instantly get bar count, total length, total weight, waste-adjusted weight, and estimated cost — plus an SVG layout diagram.
Rebar Calculation Formulas
Longitudinal bar count = floor((slab width − 2 × edge clearance) / spacing) + 1
Transverse bar count = floor((slab length − 2 × edge clearance) / spacing) + 1
Per-bar length (longitudinal) = slab length − 2 × edge clearance + lap splice
Per-bar length (transverse) = slab width − 2 × edge clearance + lap splice
Total weight = total length × unit weight per length (lb/ft or kg/m)
Unit weight is calculated as W = 0.00617 × d² (d = diameter in mm, result in kg/m), or looked up from standard ASTM A615 tables for imperial sizes.