Bar Bending Schedule: cutting lengths, hooks and lap rules explained

A bar bending schedule (BBS) converts structural drawings into a procurement list: bar mark, diameter, shape, number of bars, cutting length and weight. Getting it right is the difference between a tight steel budget and 8–12% of avoidable wastage.

Cutting length is never the same as the member span. You add hooks (typically 9d per hook) and laps (typically 50d for tension laps), then deduct for bends because steel stretches around the mandrel: 2d for each 45° bend, 2d for each 90° bend and 3d for each 135° hook in a stirrup.

Unit weight comes from the classic d²/162 relation, giving kilograms per metre for a given diameter in millimetres. A 12 mm bar therefore weighs 0.889 kg/m; multiply by cutting length and quantity for the bar mark total.

For stirrups, work from the clear dimensions: subtract twice the clear cover from both the width and depth of the member, take the perimeter, add two hooks and deduct the bends. Under-deducting here is the single most common BBS error we see on audit.