Rebar Calculator
Enter the slab size and grid spacing to get the total linear feet of rebar and the number of standard bars for a two-way grid.
Slab & grid
Assumes a two-way grid. Add ~10–15% for laps and overlap on long runs.
You'll need
Bars across width0
Bars across length0
Total rebar
0 ft
0 × 20 ft bars
Add tie wire and chairs/dobies. Lap splices add length — order ~10% extra on big pours.
How to estimate rebar
Count the bars in each direction from the spacing, multiply by the run length, and sum. Divide by the bar stock length for piece count, and add 10–15% for lap splices and waste. Always defer to engineered drawings.
Lay out slabs and footings from a scan
ProBuildCalc turns your iPhone's LiDAR scanner into a job-site measuring kit — walk the space and it captures the square footage, material takeoff, and a blueprint automatically. No tape measure, no graph paper.
Rebar calculator FAQ
- How do I calculate rebar for a slab?
- For a two-way grid, count bars in each direction: divide the slab width in inches by the spacing and add one for the bars running lengthwise, and do the same the other way. Multiply each count by the run length and add the two totals for linear feet.
- What spacing should rebar be?
- Residential slabs commonly use #3 or #4 bar at 12 to 18 inches on center, but always follow the engineered drawings or local code for your specific slab and loads.
- How long are standard rebar lengths?
- Rebar is commonly stocked in 20-foot lengths, with 10-foot also available. Divide your total linear feet by the stock length and round up.
- Do I need extra rebar for laps?
- Yes. Where bars overlap (lap splices), you lose length, typically 40 bar diameters. Add about 10–15% to your linear footage on larger pours to cover laps and waste.