Cubic Meters / Hour (m³/h)
Cubic Meters / Second (m³/s)
Liters / Minute (L/min)
US Gallons / Minute (GPM)
Meters / Second (m/s)
Feet / Second (ft/s)
Calculated Results
Required Internal Diameter (ID):
0 Millimeters (mm)
0 Inches (in)
0 Meters (m)
Note: This is the internal diameter. Always select the next standard pipe size up.
How to Calculate Pipe Diameter from Flow Rate
In hydraulic engineering and piping design, determining the correct pipe diameter is crucial for system efficiency. Selecting a pipe that is too small leads to high pressure drops, noise, and erosion, while a pipe that is too large increases material and installation costs.
The Fundamental Formula
The relationship between flow rate, pipe area, and velocity is defined by the continuity equation:
Q = A × v
Where:
Q: Volumetric Flow Rate
A: Internal Cross-sectional Area of the pipe (πd²/4)
v: Fluid Velocity
By rearranging the formula to solve for diameter (d), we get:
d = √[(4 × Q) / (π × v)]
Recommended Flow Velocities
When designing a system, engineers typically use "rule of thumb" velocities to prevent cavitation and minimize friction losses:
Fluid Type
Typical Velocity (m/s)
Typical Velocity (ft/s)
Water (Suction)
0.5 – 1.5
1.6 – 4.9
Water (Delivery)
1.5 – 3.0
4.9 – 9.8
Compressed Air
15 – 30
50 – 100
Steam (Saturated)
20 – 40
65 – 130
Step-by-Step Calculation Example
Suppose you have a water pump delivering 50 m³/h and you want to maintain a velocity of 2.0 m/s.