Handbook›Standard Hook & Bend Lengths

Standard Hook & Bend Lengths

IS 2502:1999 · Clause 5.3 — Hooks, bends, and minimum bend radii for reinforcement bars

Standard hook and bend lengths for deformed (TMT) and mild steel reinforcement bars as per IS 2502:1999 (Bending & Fixing of Bars for Concrete Reinforcement). Minimum internal bend diameter is 4d for bars ≤20 mm and 5d for bars >20 mm. Hook length (180°) = 16d, Bend length (90°) = 8d, Stirrup bend (135°) = 10d. All values assume Fe 415/Fe 500 TMT bars unless noted.

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Standard Hooks (180°)

Hook length = 16d; min internal bend dia = 4d (≤20 mm) or 5d (>20 mm)

Bar Dia	Min Bend Dia	Hook Length	Bend Length	Note
6 mm	24 mm (4d)	96 mm	—	Stirrups & links
8 mm	32 mm (4d)	128 mm	—	Stirrups & links
10 mm	40 mm (4d)	160 mm	—	Small beams, slabs
12 mm	48 mm (4d)	192 mm	—	Common for slab main bars
16 mm	64 mm (4d)	256 mm	—	Beam & column main bars
20 mm	80 mm (4d)	320 mm	—	Beam & column main bars
25 mm	125 mm (5d)	400 mm	—	Heavy beams, footings
32 mm	160 mm (5d)	512 mm	—	Heavy columns, pile caps
36 mm	180 mm (5d)	576 mm	—	Rarely used; check coupler option
40 mm	200 mm (5d)	640 mm	—	Very heavy sections; mechanical splices preferred

Standard Bends (90°)

Bend length = 8d; min internal bend dia = 4d (≤20 mm) or 5d (>20 mm)

Bar Dia	Min Bend Dia	Hook Length	Bend Length	Note
6 mm	24 mm (4d)	—	48 mm	Stirrups & ties
8 mm	32 mm (4d)	—	64 mm	Stirrups & ties
10 mm	40 mm (4d)	—	80 mm	Distribution bars
12 mm	48 mm (4d)	—	96 mm	Slab & beam bars
16 mm	64 mm (4d)	—	128 mm	Beam bottom bars
20 mm	80 mm (4d)	—	160 mm	Beam & column bars
25 mm	125 mm (5d)	—	200 mm	Heavy beams, footings
32 mm	160 mm (5d)	—	256 mm	Heavy columns, piles
36 mm	180 mm (5d)	—	288 mm	Check cold bending feasibility
40 mm	200 mm (5d)	—	320 mm	Mechanical anchorage preferred

Standard Bends (135° for Stirrups)

Bend length = 10d beyond the bend; min internal bend dia = 4d (≤20 mm) or 5d (>20 mm)

Bar Dia	Min Bend Dia	Hook Length	Bend Length	Note
6 mm	24 mm (4d)	—	60 mm	Light stirrups, slab links
8 mm	32 mm (4d)	—	80 mm	Standard stirrup size
10 mm	40 mm (4d)	—	100 mm	Common stirrup for beams
12 mm	48 mm (4d)	—	120 mm	Heavy shear zones
16 mm	64 mm (4d)	—	160 mm	Large beam stirrups
20 mm	80 mm (4d)	—	200 mm	Rarely used as stirrups
25 mm	125 mm (5d)	—	250 mm	Not typical for stirrups
32 mm	160 mm (5d)	—	320 mm	Not recommended for stirrups
36 mm	180 mm (5d)	—	360 mm	Not used as stirrups
40 mm	200 mm (5d)	—	400 mm	Not used as stirrups

Notes

• All hook and bend lengths are measured along the centre-line of the bar from the start of the bend to the free end

• For mild steel (Fe 250), minimum bend diameter can be reduced to 2d, but TMT bars (Fe 415/500/550) must follow 4d/5d rule strictly

• TMT bars >20 mm diameter are harder to bend on site — always use a bar bending machine, never heat the bar to bend it

• Heating TMT bars destroys the tempered martensite layer and drastically reduces yield strength — this is a common site malpractice

• Cutting tolerance: ±25 mm on straight lengths, ±15 mm on bent dimensions per IS 2502 Clause 4.3

• 135° hooks are mandatory for stirrups in earthquake-resistant design (IS 13920) — 90° hooks open up under reversed cyclic loading

• For bundled bars, the minimum bend diameter is based on the equivalent diameter of the bundle, not individual bar diameter

• Always add 2d to 3d extra length (wastage allowance) when ordering cut & bent steel from the supplier

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