Volume Flow Calculator
Calculate volumetric flow rate using pipe diameter and velocity, area and velocity, or volume over time.
What is volume flow rate?
Volume flow rate (also called volumetric flow rate) describes how much fluid passes through a section per unit time. It is commonly written as Q and measured in units like m³/s, L/min, or CFM. Engineers use it in HVAC systems, plumbing design, pump selection, process lines, and lab testing.
Core formulas used in this calculator
1) From pipe diameter and velocity
Q = A × v, where A = πd²/4
- Q = volume flow rate
- A = cross-sectional area
- v = average flow velocity
- d = inner diameter of the pipe
2) From known area and velocity
If area is already known (for ducts, channels, or custom geometries), multiply area by average velocity directly: Q = A × v.
3) From measured volume and elapsed time
In practical testing, you can collect a known volume and divide by time: Q = V / t.
How to use the calculator
- Select a method at the top of the calculator.
- Enter positive values only.
- Choose matching units for each entry.
- Click Calculate Flow Rate.
- Read outputs in m³/s, L/s, L/min, m³/h, and CFM.
Example applications
Pump line sizing
Suppose you have a 50 mm pipe and average velocity of 2 m/s. The calculator computes area from diameter, then returns flow rate immediately. This helps you compare pump curves and pressure-loss estimates.
HVAC airflow checks
For a rectangular duct converted to equivalent area, input area and measured air velocity to estimate volumetric airflow and convert to CFM for field balancing work.
Container fill/empty tests
If a tank fills by 120 liters in 45 seconds, the volume/time method provides the average flow rate without needing pipe dimensions.
Common mistakes to avoid
- Using outer pipe diameter instead of inner diameter.
- Mixing incompatible units without conversion.
- Assuming point velocity equals average velocity across the section.
- Ignoring that real systems may vary with pressure, temperature, and viscosity.
Quick unit guidance
A few useful conversions:
- 1 m³/s = 1000 L/s
- 1 m³/s = 60,000 L/min
- 1 m³/s = 3600 m³/h
- 1 m³/s ≈ 2118.88 CFM
FAQ
Is this for liquids only?
No. The equations apply to liquids and gases for volumetric flow, as long as your velocity and area are valid.
Does this include pressure drop?
No. Pressure drop requires additional data such as pipe length, roughness, fluid properties, and fittings.
Can I use this for non-circular ducts?
Yes. Use the Area + Velocity method and enter the actual cross-sectional area.