Flow Rate Formula
Calculate the volume of fluid passing through a pipe or channel per unit time.
Essential for plumbing and hydraulics.
The Formula
Q = A × v
Flow rate is the volume of fluid that passes through a cross-section per unit time. It equals the cross-sectional area of the flow multiplied by the fluid velocity.
Variables
| Symbol | Meaning |
|---|---|
| Q | Volumetric flow rate (m³/s or liters/min) |
| A | Cross-sectional area of the pipe or channel (m²) |
| v | Average fluid velocity (m/s) |
Example 1
Water flows through a 5 cm diameter pipe at 2 m/s. Find the flow rate.
r = 0.025 m
A = π × (0.025)² = π × 0.000625 = 0.001963 m²
Q = 0.001963 × 2
Q = 0.00393 m³/s ≈ 3.93 liters/s ≈ 236 liters/min
Example 2
A rectangular channel (0.3 m × 0.2 m) carries water at 1.5 m/s
A = 0.3 × 0.2 = 0.06 m²
Q = 0.06 × 1.5
Q = 0.09 m³/s = 90 liters/s
When to Use It
Use the flow rate formula when:
- Sizing pipes for water supply or drainage systems
- Calculating how long it takes to fill a tank
- Designing irrigation and cooling systems
- Measuring river or stream discharge