Stirrup Length and Count Calculator
Stirrup length, count and weight with the 11.9d seismic hook allowance.
Quick answer
With the default inputs: Section width 300 · Section depth 600 · Concrete cover 25 etc.Length per stirrup 1790 mm
Edit the inputs below to recalculate.Inputs
Result
Length per stirrup
1790mm
| Outer width | 250mm |
| Outer depth | 550mm |
| Outer perimeter | 1600mm |
| Weight per stirrup | 0.707kg |
| Number of stirrups | 31bars |
| Total length | 55.5m |
| Total weight | 21.9kg |
| Weight per metre | 3.65kg/m |
Assumes 135° hooks at both ends, 11.9d each. Confinement zones use closer spacing and are not modelled here; the actual schedule must separate confined and non-confined lengths by seismic class.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Outer dimensions | b' = b − 2c, h' = h − 2c |
| Perimeter | U = 2 × (b' + h') |
| Length per stirrup | L = U + 2 × 11.9d (seismic 135° hooks) |
| Count | n = floor(member length ÷ spacing) + 1 |
| Unit weight | 0.00617 × d² kg/m |
A 300 × 600 beam with 25 mm cover, Φ8 stirrups at 200 mm over 6000 mm: 1600 mm perimeter, 1790 mm per stirrup, 31 stirrups, 55.5 m total and 21.9 kg.
How to work it out
- Work out the inside dimensions: b' = b − 2c and h' = h − 2c, where c is the cover.
- Perimeter U = 2 × (b' + h'). This is the simplified inside-dimension convention that matches site cutting.
- Add hooks: a seismic 135° hook adds 11.9d each (10d straight tail plus the bend), so 2 × 11.9d in total.
- Bar length L = U + 2 × 11.9d, with the tail not less than 10d and not less than 75 mm.
- Count n = ⌊length ÷ spacing⌋ + 1, measuring the confined zones separately at their closer spacing.
Where it goes wrong
- Using 6.25d for the hooks — 6.25d is a 180° hook for plain round bar ends; a seismic stirrup hook is 135° and adds 11.9d, so the wrong figure is over 5d short.
- Mixing centreline lengths and bend deductions — most quantity systems use inside perimeter plus 2 × 11.9d, which matches site cutting; mixing conventions makes the two never reconcile.
- Ignoring the confined zones — column stirrups at 100 mm near the ends and 200 mm elsewhere; running 200 mm throughout halves the count.
Material and cost
Stirrups are 15-25% of the steel in a frame, second only to main bars. Φ8 is about 1.6 per metre; a 300×600 beam at six stirrups per metre of 1.9 m is roughly 18 per metre of beam.
On site
- Calibrate the cut length on the bender; different bend radii change the deduction, so bend the first piece and check.
- Both 135° hook tails must be parallel and turned inward — a mandatory seismic inspection item.
- Measure inner links and crossties separately; a four-leg stirrup has inner links of a different length from the outer.
Basis
- GB 50010-2010 Code for design of concrete structures, Section 9.2 (stirrup detailing) and Section 11.4 (seismic stirrups)
- GB 50666-2011 Code for construction of concrete structures, Section 5.3 (bar fabrication)
- 16G101-1 Standard drawings for flat-slab detailing, page 62
FAQ
Where does 11.9d come from?
The developed length of a 135° hook is a 10d straight tail plus the arc around a 2.5d bend, less the bend deduction — 11.9d in total. The 10d tail is mandatory in seismic detailing; non-seismic work uses 5d, hence the 5.5d figure. Short hooks are a classic earthquake failure.
How do confined and non-confined zones differ?
They are calculated separately. Beam confinement extends 2h and at least 500 mm for class I, at min(h/4, 8d, 100 mm) spacing, with non-confined spacing typically double. Column confinement takes the greater of clear height/6, the long section dimension and 500 mm. This calculator uses one spacing throughout.
Can stirrup diameter be chosen freely?
No. The code requires at least d/4 of the largest longitudinal bar and not less than 6 mm, and 8 mm where the beam is wider than 800 mm, plus a minimum shear reinforcement ratio — seismic volumetric ratios are tabulated by axial load ratio and class. Undersized stirrups cause shear failure before flexural yield, which is brittle.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Stirrup Length and Count Calculator. 2026-10-25. https://jianzhujisuan.com/en/rebar-stirrup
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.