Mass Flow Rate Calculator
By Santaji GadepatilinUpdated October 27, 2026
How to use this calculator
Enter the volumetric flow and density to get mass flow, or enter the mass flow to get volume. Every field has its own units.
The formula
ṁ = ρ × Q
Worked example
50 m³/h of water at 20 °C (998 kg/m³):
ṁ = 998 × 50 = 49,900 kg/h = 49.9 t/h = 13.86 kg/s
Density changes with temperature
Water is 998 kg/m³ at 20 °C but about 965 kg/m³ at 90 °C. A volumetric meter reading the same m³/h at 90 °C represents about 3% less mass. For oils and fuels the effect is larger — around 0.07–0.1% per °C.
Typical densities
| Fluid | kg/m³ |
|---|---|
| Water (20 °C) | 998 |
| Diesel | ~835 |
| Milk | ~1,030 |
| Air (20 °C, 1 atm) | 1.204 |
| Natural gas (standard) | ~0.75 |
Frequently asked questions
How do I convert m³/h to kg/h?
Multiply by the density in kg/m³. 50 m³/h of water (998 kg/m³) is 49,900 kg/h.
Why use mass flow instead of volume?
Mass does not change with temperature or pressure, while volume does. Billing, batching and chemical dosing usually rely on mass.
Which flow meters measure mass directly?
Coriolis meters measure mass flow directly. Thermal mass meters do for gases. Others measure volume and need density to calculate mass.