Structural caveat
This is not a structural design tool. Rebar size, placement, lap length, cover and spacing should follow engineering drawings and local building requirements.
Example
For a 20 ft by 12 ft slab with 18 inch spacing, the grid needs bars in both directions. The calculator counts rows from spacing, multiplies by bar length, then applies layers and waste allowance.
Common mistakes
Do not confuse spacing in inches with slab dimensions in feet. Also remember laps, edge cover, chairs and stock bar lengths when ordering material.
Limitations
This calculator estimates linear feet only. It does not determine structural adequacy, rebar diameter, concrete strength, code compliance or engineering details.
Last reviewed: 2026-05-17