Rebar Spacing and Quantity

Linear feet of rebar from slab dimensions and spacing.

Run the calculator

Example

You enter

Length (ft) 20
Width (ft) 10
Spacing on center (in) 12
Edge clearance (in) 3
Bar size #4

You get

Bars (along length) 10
Bars (along width) 20
Total linear feet 385

Details, formula, and sources

Bars per direction = floor((dimension - 2 × cover) / spacing) + 1; total length = bars × dimension + lap-splice allowance per ACI 318 §25.5.

ACI 318-19 (Building Code Requirements for Structural Concrete) by name. IBC 2021 (International Building Code). §1905 references ACI 318.

ACI 318 licensed; principles free in published engineering texts.

Estimate. AHJ and licensed structural engineer govern.

Field names used by the API: length_ft, width_ft, spacing_in, edge_clearance_in, bar_size, bars_along_length, bars_along_width, total_length_ft

Default cover 2 in (concrete cast against earth) unless user suppliesACI 318 §20.5.1.3
Default lap splice 40 × bar diameter for #5 and smaller (Class B)ACI 318 §25.5