Rebar Bend Deduction Calculator
How much to deduct per bend when converting out-to-out to centreline length.
Inputs
Result
Formula
| Deduction = k × d | k = 0.35 / 0.50 / 0.85 / 2.00 / 2.50 by angle |
| Per bar = deduction × bends | |
| Total = per bar × number of bars | |
| Unit weight = 0.00617 × d² | kg/m, d in mm |
100 bars of Φ20 with two 90° bends each: 40 mm per bend, 80 mm per bar, 8.0 m total; at 2.468 kg/m that is 19.7 kg of over-ordering if the deduction is ignored.
FAQ
Why 2d for a 90° bend?
Out-to-out dimensions run along two tangents meeting at the corner, while the bar follows an arc. With a 4d bend diameter the arc centreline is about 2d shorter. A stirrup with four 90° bends would be 8d too long without the deduction - it simply would not fit in the formwork.
How do I handle a 135° stirrup hook?
In two steps: take the 135° bend deduction here (2.5d), then add the straight tail separately (at least 10d and not less than 75 mm for seismic detailing). Stirrups are usually cut to outside dimensions while longitudinal bars are measured on the centreline - mixing the two introduces a systematic error.
Does it really matter on site?
Per bar it is small, but at scale it is tonnes of over-ordering per floor, and worse, the wrong size will not fit - so crews bend or cut it on site and damage the steel. Bend deductions belong on every bar list.
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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.