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Flow Rate Calculator

Free online flow rate calculator to calculate volumetric flow rate, velocity, and pipe area. Convert between m³/h, L/min, GPM, and CFM. Essential for plumbing, HVAC, and fluid systems.

The Flow Rate Calculator helps you calculate volumetric flow rate, flow velocity, and pipe cross-sectional area. Enter any two parameters to calculate the third. Supports multiple units for water, air, and other fluids.
What to Calculate
Q = v × AQvDFlow Rate = Velocity × Area

What is Flow Rate?

Flow rate (also called discharge rate or volumetric flow rate) is the volume of fluid that passes through a given surface per unit time. It's expressed in units like cubic meters per hour (m³/h), liters per minute (L/min), gallons per minute (GPM), or cubic feet per minute (CFM). Flow rate is calculated by multiplying the flow velocity by the cross-sectional area of the pipe or duct. Understanding flow rate is essential for sizing pipes, pumps, valves, and designing efficient fluid systems in plumbing, HVAC, hydraulics, and process engineering.

Flow Rate Formulas

1. Flow Rate (Q) = Velocity (v) × Area (A)

2. Area (A) = π × (Diameter/2)²

3. Velocity (v) = Flow Rate (Q) / Area (A)

4. Diameter (D) = 2 × √(Area / π)

Typical Flow Velocities

Water (Residential): 1-2 m/s (3-6 ft/s)

Water (Commercial): 1.5-3 m/s (5-10 ft/s)

Air Ducts (Supply): 3-8 m/s (600-1600 fpm)

Air Ducts (Return): 2-5 m/s (400-1000 fpm)

Steam: 15-30 m/s (3000-6000 fpm)

Flow Rate Unit Conversions

1 m³/h = 16.67 L/min = 4.40 GPM = 0.588 CFM

1 GPM = 3.785 L/min = 0.227 m³/h = 0.134 CFM

1 CFM = 28.32 L/min = 1.699 m³/h = 7.48 GPM

Applications

  • Plumbing: Water supply design, fixture flow requirements
  • HVAC: Air flow calculations, ventilation rates, duct sizing
  • Fire protection: Sprinkler flow rates, hydrant capacity
  • Irrigation: Water delivery systems, drip line sizing
  • Industrial: Process fluid systems, chemical dosing
  • Hydraulics: Hydraulic circuit design, actuator speed
  • Aquariums: Filtration flow rates, pump selection

Tips for Flow Rate Calculations

  • Too high velocity causes noise, erosion, and excessive pressure drop
  • Too low velocity may cause settling of particles or insufficient mixing
  • Account for peak flow conditions, not just average flow
  • Use flow meters for critical applications requiring monitoring
  • Consider future expansion when sizing pipes
  • Velocity in suction lines should be lower than discharge lines
  • Check local codes for minimum flow rates in plumbing fixtures
See also
ENGINEERING CALCULATORS
WUTOOLS