Pipe Flow Rate Calculator
Calculate volumetric flow rate based on pipe diameter and fluid velocity.
Calculation Results
Understanding the Pipe Flow Rate Calculation Formula
Determining the volumetric flow rate of a fluid moving through a pipe is a fundamental task in fluid dynamics, civil engineering, and process plant design. Whether you are designing a municipal water supply, an irrigation system, or an industrial chemical loop, understanding the relationship between the pipe's size, the velocity of the fluid, and the resulting flow rate is essential.
The Core Formula
The flow rate ($Q$) is calculated based on the continuity equation, which states that the volumetric flow rate is equal to the cross-sectional area of the pipe multiplied by the average velocity of the fluid.
Where:
- Q = Volumetric Flow Rate (e.g., m³/s, GPM)
- A = Cross-Sectional Area of the pipe (m² or ft²)
- v = Average Fluid Velocity (m/s or ft/s)
Calculating the Cross-Sectional Area
Since pipes are cylindrical, the area ($A$) is calculated using the formula for the area of a circle based on the pipe's internal diameter ($D$):
Important Note: Always ensure your units match. If your velocity is in meters per second, your diameter must be converted to meters before calculating the area.
Practical Example
Let's say you have a pipe with an internal diameter of 100 mm (0.1 meters) and water flowing at a velocity of 2 meters per second.
- Calculate Area: Radius = 0.05m. Area = π × 0.05² ≈ 0.00785 m².
- Calculate Flow (Q): 0.00785 m² × 2 m/s = 0.0157 m³/s.
- Convert Units:
- To m³/h: 0.0157 × 3600 ≈ 56.5 m³/h
- To Liters/min: 0.0157 × 60000 ≈ 942 L/min
Why Velocity Matters
Keeping fluid velocity within a specific range is crucial. If the velocity is too high, it causes excessive friction loss (pressure drop), noise, and potential pipe erosion. If the velocity is too low, it may lead to sedimentation (solids settling) or require unnecessarily large and expensive piping. Typical design velocities for water range from 1.0 m/s to 3.0 m/s depending on the application.