Rebar Spacing and Quantity
Linear feet of rebar from slab dimensions and spacing.
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
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
Formula or tableBars per direction = floor((dimension - 2 × cover) / spacing) + 1; total length = bars × (dimension - 2 × cover). No lap-splice allowance is added; bars longer than stock length need laps per ACI 318 §25.5.
Source and editionACI 318-19 (Building Code Requirements for Structural Concrete) by name. IBC 2021 (International Building Code). §1905 references ACI 318.
Free accessACI 318 licensed; principles free in published engineering texts.
What governsEstimate. AHJ and licensed structural engineer govern.
API field nameslength_ft, width_ft, spacing_in, edge_clearance_in, bar_size, bars_along_length, bars_along_width, total_length_ft
- Default cover 3 in (concrete cast against and permanently in contact with earth) unless user suppliesACI 318-19 Table 20.6.1.3.1
- Lap splices not included in the total; add laps where a run exceeds the stock bar length (Class B tension lap per ACI 318 §25.5)ACI 318 §25.5