Bending and shape codes
BS 8666 cutting length by shape code (00, 11, 12, 13, 21, 25, 26, 31, 32, 33, 41, 51, 63)
- where
- cutting length for each BS 8666 shape code (mm)
- scheduled outside dimensions (mm)
- bend radius: BS 8666 minimum for the bar size unless entered; R for shape 12 (mm)
- bar diameter (mm)
- mass per bar (kg)
- cutting length of the selected shape (mm)
Explain this equation
Works out the cutting length of a bent bar from its BS 8666 shape code and scheduled dimensions. Use it to check a bending schedule or to cut and bend a bar on site.
A to E are the outside dimensions shown on the schedule for that shape. r is the bend radius (the BS 8666 minimum for the bar size unless a larger one is stated) and d the bar diameter. Each shape has its own equation, and m is the weight of one bar.
Adding outside dimensions overstates the length because each bend is rounded, not square. Each equation adds the straight dimensions and then takes off an allowance per bend in terms of r and d: 0.5r + d per 90° bend, which is why shape 21 with two bends loses r + 2d. Factors such as 0.57 and 1.7 come from the geometry of semicircular hooks.
Sense check: an L-bar (shape 11) 600 by 400 mm in 12 mm bar cuts at 976 mm. A link (shape 51) is about twice the sum of A and B, plus the hooks, less around 100 mm.
Watch out: use the BS 8666 shape number, not an old BS 4466 or foreign code, and keep legs at least P long.
Works out the cutting (total) length of a bent bar from its BS 8666 shape code and scheduled dimensions, for checking a bar bending schedule or cutting bars on site.
Enter your values to see the result.
Good to know
Scheduled dimensions are outside dimensions. The formulae deduct an allowance for each bend based on the minimum scheduling radius r for the bar size (BS 8666 Table 2), so leave the radius at 0 unless the schedule states a larger one. The dimension shown in brackets on the BS 8666 shape (the free dimension) is the one that takes up any cutting and bending tolerance. Shapes 25 and 26 are approximate when bend angles exceed 45°; for 13 and 33 the bend width B must be at least the hook diameter q. Shape 51 is a closed link with two hooks (C), shape 63 a closed link lapped along B.
Common mistake
Using an old BS 4466 shape number or a different country’s code (shape 51 in another code is not the same bar), or adding the dimensions without the bend deductions.
Limits
BS 8666:2020 Table 5 length formulae for B500 bars at the standard radius (or the radius entered). Bends of other angles, shape 99 and non-standard shapes need the full geometry. Five or more bends may not be achievable within tolerance.
Sources
- 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)
- Coen Steel, Shape Codes BS 8666:2020 (total length formula for each shape code)
- Heaton Manufacturing, UK rebar shape codes (total length formulae; minimum radius, former and end projection table)
- Collins Reinforcements, BS 8666 shape codes (dimension rules: free dimensions in brackets, A and end legs not less than P; minimised links 51 and 63)
- KB Rebar, BS 8666:2020 shape codes sheet (Table 2: r, M, P, links P, hook diameter q = 3d + 2r rounded up to 5 mm)
- RebarCalcPro, BS 8666 shape code 51 worked example (300 × 500 beam, 25 mm cover, H10 link, C = 100 mm, r = 20 mm: L = 1500 mm)
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.