Ductulator
Use our free online Ductulator to calculate velocity, pressure drop, Reynolds number, and friction factor based on duct type, flow rate, and air properties.
Choose circular or rectangular duct shapes
Input flow rate, and pick temperature and roughness
Use metric or imperial units
Download a professional PDF report with your results
| Parameter | Value |
|---|---|
| Velocity: | -- m/s |
| Reynolds Number: | -- |
| Friction Factor: | -- |
| Pressure Drop: | -- pa/m |
What Is A Ductulator & Why Use One?
A Ductulator is a tool used to size air ducts and assess airflow in HVAC systems. It simplifies complex calculations by letting you quickly determine how duct dimensions, airflow, and material properties impact performance.
When you use a ductulator calculator, you save time on system design and reduce the risk of errors from manual lookups or interpolation. Whether you're working on commercial or residential HVAC systems, exact duct sizing improves energy efficiency, noise levels, and system balance.
Using an online ductulator like h2x means your results are accurate, fast, and formatted for professional use; no more flipping between charts, spreadsheets and formulas.
Ductulator Variables
Duct Type
Select from Circular or Rectangular duct shapes. Your choice affects how friction and velocity are calculated.
Duct Dimensions
Input width and height for rectangular ducts or diameter for circular. Smaller ducts create higher velocities and pressure drops.
Flow Rate
The air volume moving through the duct. It's a key input that affects all other calculations like velocity and pressure drop.
Air Temperature
Choose a standard temperature of the air going through the duct. This impacts the air's viscosity and density.
Kinematic Viscosity & Density
These are auto-filled based on your selected temperature. They affect the Reynolds number and the pressure drop through the system.
Material Roughness
Choose the duct material, such as steel, brick or glass, to apply the correct roughness factor. This influences pressure loss and friction.
Ductulator Formula
The Ductulator uses standard fluid dynamics equations to calculate velocity, pressure drop, Reynolds number, and friction factor.
See how to calculate these in both imperial and metric units below:
Velocity Calculation
Imperial Equation
Following the formula below, you can calculate the velocity:
Components:
V = Velocity (ft/s)
Q = Flow rate (CFM)
A = Cross-sectional area (in²)
Metric Equation
Following the formula below, you can calculate the velocity:
Components:
V = Velocity (m/s)
Q = Flow rate (L/s)
A = Cross-sectional area (m²)
Velocity helps determine if the air is moving too slowly (inefficient) or too fast (noisy or energy-intensive).
Reynolds Number Calculation
Imperial Equation
Following the formula below, you can calculate the Reynolds number:
Components:
Re = Reynolds number (dimensionless)
V = Velocity (ft/s)
D = Hydraulic diameter (ft)
ν = Kinematic viscosity (ft²/s)
Metric Equation
Following the formula below, you can calculate the Reynolds number:
Components:
Re = Reynolds number (dimensionless)
V = Velocity (m/s)
D = Hydraulic diameter (m)
ν = Kinematic viscosity (m²/s)
Reynolds number determines whether flow is laminar or turbulent, which influences friction and energy loss.
Pressure Drop Calculation
Imperial Equation
Following the formula below, you can calculate the pressure drop:
Components:
ΔP = Pressure drop (psi)
f = Friction factor (dimensionless)
L = Duct length (ft)
D = Hydraulic diameter (in)
ρ = Air density (lb/ft³)
V = Air velocity (ft/s)
144 = Conversion factor from lb/ft² to psi
12 = Converts feet to inches for consistency in units
Metric Equation
Following the formula below, you can calculate the pressure drop:
Components:
ΔP = Pressure drop (Pa)
f = Friction factor (dimensionless)
L = Duct length (m)
D = Hydraulic diameter (m)
ρ = Air density (kg/m³)
V = Air velocity (m/s)
These equations calculate pressure drop in psi or Pa based on your unit system, helping ensure ducts are neither undersized nor oversized.
Ductulator Calculations In h2x
h2x replaces traditional ductulators with a modern design platform featuring intuitive drawings, automated calculations, and flexible exports.
Why engineers and contractors use h2x:
Smart Layouts: Draw and adjust systems quickly with auto-connected components.
Verified Sizing: Create accurate, CIBSE-verified calculations that update instantly.
Easy Exports: Generate branded PDFs or AutoCAD and Revit files in one click.
Detailed Reports: Get ductwork summaries and bills of materials for easy reviews.
