Schedules, cutting and pricing
Cutting from 12 m stock bars: pieces per bar, bars needed and waste
- where
- pieces from each stock bar
- stock bar length (m)
- cutting length of each piece (mm)
- stock bars needed
- number of pieces needed
- offcut from each full bar (mm)
- waste (%)
Explain this equation
Works out how many pieces of one cutting length come out of each stock bar, how many stock bars to order and how much is wasted.
S is the stock bar length (usually 12 m) and Lc the length of each piece. p is the number of whole pieces per stock bar, N the pieces you need and Nb the stock bars to order. o is the offcut left on each full bar and w the overall waste.
Pieces per bar are rounded down (the ⌊ ⌋ brackets) because a part piece is no use. Stock bars are rounded up because you cannot buy part of one. Waste compares the total length bought with the total length used. The 1000 converts metres to millimetres, and there is no kerf because bar is sheared.
Sense check: 2.6 m pieces from 12 m bars give four per bar with 1.6 m left over, about 13 per cent waste. Pieces just over 6 m give one per bar and nearly half is wasted.
Watch out: use offcuts for shorter bar marks to cut the real waste.
Works out how many pieces of one cutting length come out of a stock bar, how many stock bars to order, and how much is wasted.
Enter your values to see the result.
Good to know
Bar shears and cropping machines leave no kerf, so a 12 m bar gives as many whole pieces as fit in 12 000 mm. The waste figure includes the offcut on every bar and the unused part of the last bar. Offcuts long enough for other bar marks (starter bars, U-bars, short links) cut the waste; plan cut lists longest first. Stock lengths are commonly 6 m and 12 m.
Common mistake
Dividing the total length needed by 12 m, which ignores the offcut on every bar and under-orders.
Limits
One cutting length at a time. Mixed cut lists need a cutting plan (bin-packing) to minimise waste. Rolling mills supply to a small length tolerance.
Sources
- Celsa Steel UK, Reinforcing bars (BS 4449 B500C, CARES approved; 12 mm 0.888, 16 mm 1.579, 25 mm 3.854 kg/m; 6 m and 12 m stock lengths)
- CR Steel, Steel calculator sheet (bar mass per metre, metres per tonne, 12 m bars per tonne; BS 4483 mesh masses: A142 2.22, A193 3.02, A252 3.95, A393 6.16 kg/m²)
- BS 8666:2020 Scheduling, dimensioning, cutting and bending of steel reinforcement for concrete. Specification (Table 2 minimum radii and end projections; Table 5 standard shapes and length formulae)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.