Easy Duct

Easy Duct sizes air ducts for HVAC design, quickly and accurately. It works fully offline, with no account and no sign-up.

ENTER ANY TWO, GET THE REST
Tick any two or more of air flow, duct size, head loss and velocity, and Easy Duct calculates the others. Round and rectangular ducts are both supported, and head loss and velocity are always shown together.

CROSS-CHECK
Size a duct for two scenarios at once, such as a friction limit and a velocity limit, and Easy Duct picks the larger duct that satisfies both. Scenario B can follow scenario A by a percentage or a fixed amount.

EQUIVALENT DUCT
Convert an existing duct to another size or shape, keeping the same friction or the same velocity, and see how much friction and velocity change.

IP AND SI UNITS
Tap the unit next to any value to change it. Switch the whole app between IP and SI with one tap.

BUILDABLE SIZES
Results are rounded up to a size you can actually build, with your own size step. Metric sizes stay in whole millimetres and never show a value above your limit. Round ducts can snap to standard sizes. Results over a ticked limit turn red.

ACCURATE CALCULATIONS
- Darcy–Weisbach head loss
- Friction factor by Colebrook (default), Haaland or Altshul–Tsal
- Rectangular ducts by equivalent diameter (De, Huebscher) or hydraulic diameter (Dh)
- Velocity on the real rectangular area, as in ASHRAE
- Air density and viscosity from air temperature and altitude
- Duct roughness from a list of common materials, or your own value

DESIGN TOOLS
- Add to flow: build up the total air flow from several values
- Flow safety factor
- Spare capacity of the selected duct
- Reynolds number, friction factor, velocity pressure and required round size

MADE TO FIT YOUR SCREEN
Works on phones and tablets, in portrait and landscape. A Display size setting from 80% to 130% makes everything larger or smaller.

YOUR SETTINGS ARE REMEMBERED
Units, air conditions, roughness, friction method and size step are kept between sessions, with a Restore defaults button.

Made by a mechanical engineer, for engineers and designers. Feedback and suggestions are always welcome from the Support page.