✨ Online Ductulator

🌬️ Duct Sizer Pro

Calculate duct sizes using friction rate or velocity method. Convert between round and rectangular ducts.

📐 Duct Sizer

Unit system:
Duct type:
Size by:
Friction Rate:
in.wg / 100ft
Duct TEL:
ft * include fittings in the Duct TEL
Enter either:
CFM:
— —
— —

🔄 Rectangular → Round (Equivalent)

Side 1:
in
Side 2:
in
Equivalent round: —

🔄 Round → Rectangular (Equivalent)

Diameter:
in
Side 1:
in (enter one side to get the other)
Second side: —

ℹ️ How to Use

Duct Sizer Pro helps you size round or rectangular HVAC ducts using either Friction Rate / Head Loss or Velocity. Results update instantly—there is no calculate button.

  1. Select Unit system (Imperial or Metric). All fields convert automatically.
  2. Select Duct type (Metal, Ductboard, Flex). The tool applies the correct duct-type adjustment internally.
  3. Select “Size by”:
    • Friction rate / Head loss: enter friction and the tool returns duct size & air velocity (or, if you enter duct size, it returns airflow and velocity).
    • Velocity: enter target velocity and the tool returns duct size & head loss (or, if you enter duct size, it returns airflow and head loss).
  4. Enter either:
    • Flow: enter CFM (or L/s) to size the duct.
    • Duct size: choose Round/Rectangular, then enter diameter or sides to calculate airflow and other outputs.
  5. Use the two converters to quickly switch between Rectangular ↔ Round equivalent.
  6. Click Reset to restore defaults (unit system & duct type stay as selected).

Tip: For rectangular ducts, the sizing uses an equivalent diameter for friction calculations, while velocity is calculated from the actual rectangular area.

📚 About This Tool

This ductulator is designed for quick, practical sizing checks during HVAC design and estimating. It supports both common sizing approaches (friction rate and velocity) and includes shape conversions for easy coordination between round and rectangular duct layouts.

Always verify final selections against project specifications, codes, and applicable standards (e.g., SMACNA/ASHRAE), and consider noise criteria, fittings, and system balancing in final design.