Civil site guide

Bar bending schedule (BBS) basics: number of bars and steel weight

How a bar bending schedule works: counting bars from spacing, cutting length, steel weight per metre (d² ÷ 162) and totals by diameter, with a worked slab example.

J1 Pro · Updated 31 October 2026 · 5 min read

A bar bending schedule lists every bar mark in a member: its shape, diameter, number of bars and cutting length. From it you get the steel weight for ordering and checking.

Number of bars

Number of bars = (length available ÷ spacing) + 1 (round up) Length available = member length − 2 × cover

Steel weight

Mass per metre (kg/m) = d² ÷ 162 (d = bar diameter in mm) Weight (kg) = number of bars × cutting length (m) × kg/m

Bar diameter	kg/m	Bar diameter	kg/m
8 mm	0.395	20 mm	2.466
10 mm	0.617	25 mm	3.854
12 mm	0.888	32 mm	6.313
16 mm	1.579	40 mm	9.864

Cutting length and shape codes

BS 8666 gives each bent shape a shape code (00 = straight, 11 = one bend, 21 = U-bar, 51 = closed link, and so on) and a formula for its total length from the scheduled dimensions A, B, C… The bends use the minimum scheduling radius for the bar size (for example 2d for bars up to 16 mm and 3.5d for 20 mm and larger in grade B500), so do not simply add the dimensions shown on the drawing.

Worked example – slab bottom bars

A 4.0 m slab panel with T12 bars at 150 mm spacing, 25 mm cover, straight bars 3.95 m long.

Number of bars = (4000 − 2 × 25) ÷ 150 + 1 = 27.3 → 28 bars Mass per metre = 12² ÷ 162 = 0.888 kg/m Weight = 28 × 3.95 × 0.888 = 98.2 kg

Repeat for each bar mark, then total the weight by diameter and add an allowance for wastage and laps when ordering stock bars.

Make the schedule

The J1 Pro Bar Bending Schedule calculator uses BS 8666 shape codes, totals by diameter and member, stock bars and wastage, and prints a PDF schedule.

Open BBS calculator

Guides are for preliminary design and learning. Always verify final designs against project specifications, local codes and manufacturer data.