# Duct Support Calculator

Bracket count, steel weight, rod weight and anchors in one go.

- Page: https://jianzhujisuan.com/en/duct-support
- Category: M&E (https://jianzhujisuan.com/en/c/me)
- Chinese version: https://jianzhujisuan.com/zh/duct-support.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Duct length 30 m, Bracket spacing 3 m, Steel per bracket 1.4 m, Steel unit weight 3.77 kg/m, Rod length 0.8 m, Rod unit weight 0.617 kg/m, Rods per bracket 2 pcs, Waste allowance 5%): **Total support steel 72.4 kg**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Duct length | number | 30 | m |  |
| Bracket spacing | number | 3 | m | Code maximum 3 m horizontally, 2.5-3 m for insulated duct |
| Steel per bracket | number | 1.4 | m | Cross arm plus hangers or posts, from the detail drawing |
| Steel unit weight | number | 3.77 | kg/m | L50×5 3.77, L40×4 2.42, C5 5.44, C10 10.0 |
| Rod length | number | 0.8 | m | Slab soffit to duct top, plus adjustment |
| Rod unit weight | number | 0.617 | kg/m | φ8 0.395, φ10 0.617, φ12 0.888 |
| Rods per bracket | number | 2 | pcs |  |
| Waste allowance | number | 5 | % |  |

## Formula

- **Bracket count**: n = ⌊length ÷ spacing⌋ + 1
- **Angle steel weight**: W = n × steel per bracket × unit weight × (1 + waste)
- **Rod weight**: W = n × rods per bracket × rod length × unit weight × (1 + waste)
- **Anchors**: N = n × rods per bracket

## Worked example

30 m of duct, 3 m spacing, 1.4 m of L50×5 per bracket and two 0.8 m φ10 rods at 5% waste: 11 brackets, 60.96 kg of angle, 11.40 kg of rod, 72.4 kg total, 22 anchors and 2.41 kg per metre.

## Questions

### Why 11 brackets rather than 10?

Because both ends need support — one at the start, one at the finish, with spacing in between. 30 m divided by 3 m gives 10 spans, and 10 spans need 11 supports. This off-by-one is the most common take-off error in M&E; ordering 10 leaves you 10% short. The same spans-plus-one rule applies to pipe supports, cable tray brackets and purlins.

### Can duct hangers be anchored straight into the slab?

Yes, subject to load and slab condition. A single duct bracket usually carries tens to a few hundred kilos, and M8-M10 expansion anchors into solid concrete are standard. But hollow-core slabs, precast planks, AAC walls, pour strips or cracked slabs must use through-bolts, chemical anchors or steel straps instead. Ducts over 2000 mm and plant-room supports need a proper load calculation.

### Are seismic restraints mandatory?

For new schools, hospitals, malls and offices — densely occupied and key-defence buildings — seismic bracing of interior water, fire, HVAC and cable tray systems is mandatory under the code for seismic design of mechanical and electrical systems. Triggers are roughly pipe DN65 and above, duct section over 0.38 m², tray width over 400 mm. Bracing costs far more than ordinary supports, so omitting it from a quote is a serious loss.

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Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.