Water Flow Rate Calculator | Free Construction Calculators
Calculate water flow rate based on pipe diameter and velocity.
Typical Flow Velocities
- Cold water supply: 5-8 feet per second
- Hot water supply: 3-5 feet per second
- Drainage (gravity): 2-4 feet per second
- Fire protection: 10-15 feet per second
- Irrigation: 5-7 feet per second
Flow Rate Formula
Q = A × V
Where Q = flow rate, A = pipe area, V = velocity
A = π × r²
Recommended Flow Rates
- Kitchen sink: 2-3 GPM
- Bathroom sink: 1.5-2 GPM
- Shower: 2.5 GPM (standard), 1.8 GPM (low-flow)
- Toilet: 1.6 GPF (gallons per flush)
- Washing machine: 3-5 GPM
- Dishwasher: 1-2 GPM
Velocity Limits
- Minimum velocity: 2 fps (prevents settling in drains)
- Maximum velocity (copper): 8 fps (prevents erosion)
- Maximum velocity (PVC): 10 fps (prevents noise)
- Maximum velocity (steel): 15 fps (industrial)
Factors Affecting Flow
- Pipe diameter: Larger pipes = higher flow capacity
- Pressure: Higher pressure = higher velocity
- Friction loss: Longer runs reduce flow
- Fittings: Elbows and valves reduce flow
- Elevation changes: Uphill reduces flow
Important Notes
- High velocity causes water hammer and noise
- Low velocity allows sediment buildup in drains
- Optimal velocity balances flow rate and system longevity
- Pressure and velocity are related but not the same