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Fluid Mechanics

Mass Flow ↔ Volumetric Flow Calculator

Mass flow and volumetric flow are related by the fluid density. This calculator converts between the two when the density is known. It applies to any incompressible fluid at a specified operating condition.

TypeInteractive calculator — separate from unit conversions

Calculator

Supply the fluid density at operating conditions

Result

Density must be > 0

Formulas

Mass flow from volumetric flow
ṁ = ρ × Q
Volumetric flow from mass flow
Q = ṁ / ρ

Diagram

Mass Flow ↔ Volumetric Flow RelationshipQQρṁ = ρ × Qmass flow = density × volumetric flow

Worked example

A pump delivers 5 L/s of fluid with density 1050 kg/m³. What is the mass flow rate?

  1. 01Convert 5 L/s to m³/s: 5 × 0.001 = 0.005 m³/s
  2. 02ṁ = ρ × Q = 1050 × 0.005
  3. 03ṁ = 5.25 kg/s
Result

The mass flow rate is 5.25 kg/s.

FAQ

Does this assume a specific fluid?
No. You must supply the density. There is no hidden water or air density assumption.
Can I use this for gas flows?
Only if you provide the actual gas density at operating conditions. This calculator does not apply standard/normal gas basis conversions or compressibility corrections.
Is this a heat duty calculator?
No. This calculator only converts between mass flow and volumetric flow using density.
What density should I use?
Use the density at your actual operating temperature and pressure. For water near 20°C, approximately 998 kg/m³. For other fluids, consult your process data.