Stirrup Cutting Length Calculator: Formula & Example

Results

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Cutting length per bar

1,306mm

Total length	52.3 m
Total weight	20.6 kg
90° bend deduction	17 mm (2.07 db)

Dimensions are outside (out-to-out) as on a BS 8666 / ACI 315 bar schedule. Check your fabricator’s bending conventions.

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Working

Bar 8.0 mm, bend diameter 4.0 db
Centreline: 4 straight sides + 3 × 90° + 2 × 135° arcs (radius 20 mm) + 2 × 75 hooks = 1,306 mm
× 40 bars = 52.26 m

Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.

Formula

Outside size     A × B = member size − 2 × clear cover
Straight sides   = 2 × (A − 2(r + d)) + 2 × (B − 2(r + d))
Corner arcs      = 3 × 90° + 2 × 135° = 540° at radius rc = r + d/2
Hooks            = 2 × extension
Cutting length   = straight sides + arcs + hooks

r = bend diameter ÷ 2 (4d former: r = 2d).

Worked Example

An 8 mm stirrup for a 230 × 450 mm beam, 25 mm cover, 4d bend (32 mm), 75 mm hooks:

Outside size = (230 − 50) × (450 − 50) = 180 × 400 mm
Straight sides = 2 × (180 − 48) + 2 × (400 − 48) = 968 mm
Arcs = 540° at 20 mm radius = 3π × 20 = 188.5 mm
Hooks = 2 × 75 = 150 mm
Cutting length = 968 + 188.5 + 150 = 1,306 mm

Stirrup Cutting Length for Common Sizes

8 mm bar, 4d bend, 75 mm hooks. Beams with 25 mm cover, columns with 40 mm cover.

Member	Outside size	Cutting length
Beam 230 × 300 mm	180 × 250 mm	1,006 mm
Beam 230 × 450 mm	180 × 400 mm	1,306 mm
Beam 230 × 600 mm	180 × 550 mm	1,606 mm
Beam 300 × 600 mm	250 × 550 mm	1,746 mm
Column 230 × 230 mm	150 × 150 mm	746 mm
Column 300 × 300 mm	220 × 220 mm	1,026 mm
Column 300 × 450 mm	220 × 370 mm	1,326 mm

Check the covers, bend diameter and hook length on your drawings: change them in the calculator above.

More Cutting Lengths

Frequently Asked Questions

What is the formula for stirrup cutting length?

Cutting length = 2 × (A − 2(r + d)) + 2 × (B − 2(r + d)) + 3 × 90° arcs + 2 × 135° arcs + 2 × hook extension, where A and B are the outside sizes, d is the bar size and r the bend radius. The arcs are measured on the bar's centreline, radius r + d/2.

How do I find the stirrup size from the beam size?

Take the clear cover off each face. A 230 × 450 mm beam with 25 mm cover to the stirrup has an 8 mm stirrup 230 − 50 = 180 mm wide and 450 − 50 = 400 mm deep, measured outside.

What is the quick site formula for stirrups?

Many sites use 2 × (A + B) + 2 × 10d for the hooks − 3 × 2d for the 90° bends − 2 × 3d for the 135° bends, which comes to 2(A + B) + 8d. It ignores the real bend radius, so it can be several centimetres short: for the 180 × 400 mm example it gives 1,224 mm, against 1,316 mm exact with the same 80 mm hooks. Check which method your bar bending schedule uses.

How long should a stirrup hook be?

ACI 318 asks for a 135° hook with an extension of 6 bar diameters, at least 75 mm (3 in). In India, IS 13920 asks for 6d but at least 65 mm in earthquake-resistant members, and many sites simply use 10d (80 mm for an 8 mm bar).

Stirrup Cutting Length Calculator

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