Free tool

Duct sheet weight and spiral output calculator

Work out how much sheet and steel a rectangular duct job takes, and how many metres of spiral duct a tubeformer makes per shift. Everything runs in your browser. When the numbers look right, send them to us and an engineer sizes a line to them.

Rectangular duct sheet and weightSpiral duct outputSend your numbers

Calculator 1

Rectangular duct sheet area and weight

Flat blank size, sheet area and weight per piece and for the whole order.

Density used: galvanized steel 7.85, stainless steel 7.93, aluminium 2.70 g/cm³. The allowance is added to all four edges of the flat blank (two seam edges, two flange ends) to cover the seam and the flange.

Result

Sheet per piece
– m²
Weight per piece
– kg
Sheet, 100 pieces
– m²
Weight, 100 pieces
– kg

Flat blank –. Finished duct surface – m² per piece, before allowances.

How we calculate

The flat blank is the duct girth plus the allowance on both seam edges, by the duct length plus the allowance on both flange ends:

blank = (2×(W + H) + 2a) × (L + 2a)

weight (kg) = sheet (m²) × thickness (mm) × density (g/cm³)

Allowance a depends on the seam (Pittsburgh, snaplock) and the flange (TDF, TDC). Change it to match your shop standard. Offcuts and coil-end scrap are not included.

Calculator 2

Spiral duct output

Metres of finished spiral duct per hour and per shift, from the strip feed speed.

SBTF-1602 reference (from the product page): strip speed up to 60 m/min depending on material; strip width 137 mm for 0.4–1.0 mm and 140 mm for 1.1–1.3 mm; diameter Φ80–Φ1600 mm. Lock seam width is the part of the strip used up in the seam; with lock seam 0 and running time 100% the result is the theoretical maximum. Lower the running time for coil changes, head changes and breaks. Enter your own figures to get a planning number.

Result

Duct speed
– m/min
Per hour
– m
Per shift
– m
Duct surface per shift
– m²

Strip angle to the circumference –°, duct advance – mm per turn.

How we calculate

Unrolled, one turn of the tube is a strip of length √((πD)² + p²) and effective width we = strip width − seam. Its area equals the tube surface per turn, πD × p, so the tube advances p = we / cos α per turn, where sin α = we / (πD). Feeding strip at speed v, the duct comes out at:

duct speed = v × we / (π × D)

metres per shift = duct speed × 60 × hours × running time %

Example: Φ300 mm, 137 mm strip, 60 m/min gives 60 × 0.137 / (π × 0.300) = 8.72 m/min of duct.

Next step

Want a line sized to this output?

Send these numbers and we reply within 12 hours.

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Before you ask for a quotation

The machine that fits depends on more than output. These pages cover the rest of the decision.