Duct Friction Rate Calculator
Pa/m friction of a round galvanized duct at your airflow — the friction chart in a box.
Design mains near 0.8–1 Pa/m. Each duct size down roughly TRIPLES the friction rate at the same flow — the chart's brutal arithmetic.
Formula
Duct Friction Rate Calculator is a free duct friction rate for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Duct Friction Rate Calculator
Pa/m friction of a round galvanized duct at your airflow — the friction chart in a box. The calculation implements ΔP/L = 0.0223·Q^1.852/D^4.973 (galvanized, standard air) (ASHRAE duct friction chart (Altshul-Tsal fit)). Design mains near 0.8–1 Pa/m. Each duct size down roughly TRIPLES the friction rate at the same flow — the chart's brutal arithmetic.
How to use Duct Friction Rate Calculator
- 1Enter Airflow in L/s.
- 2Enter Duct diameter in mm.
- 3Read Friction rate, Velocity instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Duct Friction Rate Calculator?
- ✓Implements the standard formula — ΔP/L = 0.0223·Q^1.852/D^4.973 (galvanized, standard air)
- ✓Reference cited on-page: ASHRAE duct friction chart (Altshul-Tsal fit)
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Duct Friction Rate Calculator use?+
It computes ΔP/L = 0.0223·Q^1.852/D^4.973 (galvanized, standard air), per ASHRAE duct friction chart (Altshul-Tsal fit). The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Design mains near 0.8–1 Pa/m. Each duct size down roughly TRIPLES the friction rate at the same flow — the chart's brutal arithmetic.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Duct Friction Rate Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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