Work out rebar spacing instantly with clear inputs, formula shown and shareable results.
Spacing is set by how much steel area one bar contributes: 1000 mm of width divided by the required area per metre times the area of a single bar. The result is rounded down to a practical 25 mm increment and capped at the maximum spacing the code permits for crack control.
Spacing
s = 1000 x area of one bar / required steel area per metre
Provided steel
Ast provided = (1000 / s) x area of one bar
Preliminary estimate only. Reinforcement detailing must be designed and checked by a qualified structural engineer against the governing code.
s = 1000 x area of one bar / required steel area per metre. Spacing is set by how much steel area one bar contributes: 1000 mm of width divided by the required area per metre times the area of a single bar.
Widely spaced bars leave the concrete between them to crack unrestrained. Codes limit spacing to about three times the slab thickness or 300 mm, whichever is less, for crack width control.
This calculator takes 3 inputs: Steel area required, Bar diameter, Maximum permitted spacing. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.