🪝 Rebar Calculator
Enter the slab dimensions, bar spacing, and edge clearance to estimate the number of reinforcing bars in each direction and the total length of rebar for a two-way mat.
🪝 Estimate Your Rebar
What is a Rebar Calculator?
A rebar calculator estimates how many reinforcing bars a slab mat needs and how much total bar length to order. It divides each clear span by the bar spacing, counts the bars running each way, and sums their lengths into a single material figure.
Enter the slab length and width, the spacing your design calls for, and the edge cover, and the tool returns bars in each direction plus total feet of rebar. These are estimates for planning; verify with a structural engineer for load-bearing work.
❓ Frequently Asked Questions
How many rebar do I need for a slab?
Count bars in each direction by dividing the clear span (the slab dimension minus the edge cover on both sides) by the spacing, then add one for the starting bar. A 10 ft slab with 12-inch spacing and 3-inch cover gives floor((120 − 6) ÷ 12) + 1 = 10 bars in that direction, and the same the other way for a two-way mat.
What rebar spacing should I use?
Spacing comes from the structural design, not a rule of thumb — common residential slabs use 12 to 18 inches on center, while heavily loaded slabs use tighter spacing. Closer spacing means more bars and more total length. This tool shows how spacing changes the quantity so you can compare options your engineer approves.
Does this include lap splices and bends?
No. The total length is the straight run of bar in both directions and excludes lap splices, hooks, bends, and the chairs that hold the mat off the subgrade. Add an allowance for laps (often 40 to 50 bar diameters per splice) when you order, especially where bars are joined across long spans.
Are these rebar quantities exact?
They are estimates for planning; verify with a structural engineer for load-bearing work. Bar size, grade, spacing, cover, and the number of layers all come from the structural drawings — this calculator only counts a single simple mat to help you scope and price material.