Rebar Spacing and Bar Count Calculator
Bars and actual spacing from run length and design spacing, with total weight.
Inputs
Result
Formula
| Net run | L = run − 2 × cover |
| Bar count | n = floor(L ÷ spacing) + 1 |
| Actual spacing | s = L ÷ (n − 1) |
| Total weight | W = n × L × unit weight |
A 6000 mm run with 25 mm cover at 200 mm spacing, 12 mm bars: 5950 mm net gives 30 bars at 205.2 mm actual spacing, 178.5 m total and 158.5 kg.
FAQ
Why 30 bars and not 29?
Both ends carry a bar, so the count is always the number of spaces plus one. 5950 ÷ 200 = 29.75 gives 29 full spaces and therefore 30 bars. Forgetting the plus-one is the classic error, and across hundreds of beams it adds up to tonnes of steel.
How far from the edge does slab reinforcement start?
Half a spacing, not one cover. At 200 mm spacing the first bar sits 100 mm from the beam or wall face. Support moments are high at the edge and bars set too far in leave an unreinforced strip, while half a spacing is also easier to work around. Rafts and wall boundary elements follow similar rules — read the drawing notes.
Is slightly wider spacing acceptable?
Tolerances exist (typically ±10 mm and not more than 5% of design), but wider spacing means less steel per metre and lower capacity. If rounding pushes you past the tolerance, add a bar rather than spreading the spacing evenly.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.