Duct Support Calculator
Bracket count, steel weight, rod weight and anchors in one go.
Quick answer
With the default inputs: Duct length 30 m · Bracket spacing 3 m · Steel per bracket 1.4 m etc.Total support steel 72.4 kg
Edit the inputs below to recalculate.Inputs
Result
Total support steel
72.4kg
| Bracket count | 11pcs |
| Total angle length | 15.4m |
| Angle steel weight | 60.96kg |
| Total rod length | 17.6m |
| Rod weight | 11.40kg |
| Anchors required | 22sets |
| Support steel per metre | 2.41kg/m |
Count uses spacing rounded down plus one end bracket — duct ends must be supported, so 30 m at 3 m gives 11, not 10. Code limits are 3 m horizontally and 4 m vertically, tightened to 2.5-3 m for insulated duct. Grilles, dampers, access doors, elbows, tees and transitions each need their own support; those are not included above and must be added from the layout drawing.
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 |
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.
FAQ
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.
Related calculators
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.