Calculator
Steam Pipe Sizing Calculator
Calculate the required steam pipe diameter based on steam flow rate, operating pressure, and target velocity. Get the recommended nominal bore size and verify the velocity is within safe limits.
Interactive toolUpdated July 2026
Inputs
Recommended: 25–35 m/s for mains
Results
Required Pipe ID
50.0 mm
Recommended Pipe Size (NB)
75 mm
Next standard size up
Volumetric Flow
49.2 L/s
Specific volume: 0.2 m³/kg
How It's Calculated
Vol Flow = Mass Flow × Specific Volume / 3600
Area = Vol Flow / Velocity
Diameter = √(4 × Area / π) × 1000
Area = Vol Flow / Velocity
Diameter = √(4 × Area / π) × 1000
The specific volume of steam varies with pressure. At 10 bar(g), specific volume is approximately 0.177 m³/kg. At higher pressures, steam is denser (lower specific volume), so a smaller pipe can carry the same mass flow.
Velocity Guidelines
- Saturated steam mains: 25–35 m/s (max 40 m/s)
- Saturated steam branches: 20–30 m/s (max 35 m/s)
- Superheated steam mains: 30–50 m/s (max 60 m/s)
- Flash steam (two-phase): 15–20 m/s (max 25 m/s)
- Velocities above 40 m/s cause erosion, noise, and water hammer risk