Rebar Calculator
Plan a two-direction reinforcement grid with edge cover, maximum spacing, stock length and a user-specified lap. The cut schedule keeps installed lengths separate from purchased lengths and estimates mass from the supplier’s kg-per-metre value.
Your result
How the calculation works
Clear spans=dimensions−2×cover. Runs=ceil(perpendicular clear span/spacing)+1. Stock pieces per run=max(1,ceil((clear run−lap)/(stock−lap))). Cut length includes lap at every splice.
Worked example
For a 5 m × 4 m slab, 0.05 m cover and 0.2 m spacing, clear spans are 4.9 m and 3.9 m. The grid needs 21 runs along length and 26 along width: 47 stock bars when each fits a 6 m bar.
Assumptions and limitations
No offcut reuse is assumed. Bar size/mass, cover and lap are user inputs, not recommendations. Stock must exceed lap; dimensions must exceed twice the cover. Purchase count is bounded to one million bars.
Engineer approval governs reinforcement, laps, anchorage, bends, cover and splice locations. Include chairs, ties, hooks and delivery separately. This tool does not design a slab.
Sources and editorial responsibility
Maintained by Renvoro Pty Ltd. Sources inform the methods and assumptions shown here; outputs have the limitations described on this page.
Method reviewed 2026-10-13. Calculation standards · Report an issue