Bar bending schedule: cutting length, laps, hooks, bend deductions and 12 m bars

A bar bending schedule (BBS) lists every bar mark with its shape, diameter, number and cutting length. It drives fabrication on site and the most accurate rebar quantity.

Cutting length

Cutting length = straight length + hooks + laps − bend deductions

Hooks

• 90° / standard hook — commonly 9d added per hook.
• 135° seismic hook for stirrups and ties — an extension of at least 6d and 75 mm per the code; many engineers allow 10d. EstiMatrix uses max(10d, 75 mm) by default; change it in Bar bending rules.

Laps

Lap length depends on the design (tension or compression, concrete grade, bar position). Typical working values are 40d for small bars, 50d and 60d for larger ones. Always follow the structural drawings.

Bend deductions

Bending stretches the bar, so the measured length along the outside overstates the cut:

Weight

Weight = members × bars per member × cutting length × unit weight (d²/162 kg/m). See rebar weight calculation.

Stock length and offcuts

Bars are sold in 12 m (39.37 ft) lengths. Cutting lists should be packed so short pieces use offcuts of long ones; bars longer than 12 m are lapped. The difference between the theoretical weight and the gross purchase weight is the offcut percentage — keep it below about 5–8 %.

Chair bars

Top mats of slabs and rafts are supported on chairs, often 12 mm bars at around one per square metre — easy to forget, quick to add.

Doing it in EstiMatrix

The BBS sheet sets the lap automatically when you pick a diameter, adds 135° hook columns, calculates cut length and weight per row, totals by diameter, and packs cut lengths into 12 m stock bars to give a purchase requirement. Tie bars to their BOQ item, or let the rebar quantity of the BOQ come from the BBS directly.