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Free online mass flow rate calculator. Enter density and volumetric flow rate to quickly calculate mass flow rate with automatic unit conversions.
Enter values to see results
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
Mass flow rate (ṁ) is the mass passing a point per unit time. Volumetric flow rate (Q) is the volume passing per unit time, and density (ρ) is mass per unit volume. The calculator uses their relationship:
ṁ = ρ × Q
It can solve for any one of the three quantities when the other two are supplied. For example, density in kg/m³ multiplied by volume flow in m³/s gives mass flow in kg/s. The U.S. Department of Energy’s fluid-flow handbook describes this relation and the related volume-flow formula.
Available density units are kg/m³, g/cm³, g/L, and lb/ft³. Volume-flow choices are m³/s, m³/h, L/s, L/min, L/h, and US gal/min. Mass-flow choices are kg/s, kg/h, g/s, metric t/h, lb/s, and lb/h. The displayed result is converted to the selected output unit.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Select whether to solve for mass flow, density, or volume flow.
Enter the two known quantities and choose a unit for each. The third quantity is calculated as you enter valid values.
Choose the output unit for the unknown and read the result with its unit label.
Example: if density is 1,000 kg/m³ and volume flow is 0.01 m³/s, mass flow is 10 kg/s. If you select kg/h instead, the same rate is 36,000 kg/h. The number changes because the time unit changes, not because the physical flow changed.
For density mode, use mass flow and volume flow; for volume mode, use mass flow and density. A zero denominator cannot produce a defined density or volume result. The result display rounds to at most six decimal places and may use scientific notation for very small or very large values.
Use cases
See how the tool fits into real work and everyday tasks.
When a flow meter provides volume per time and a separate source provides liquid density, solve for mass flow to compare records in a mass balance or production log.
If you already know gas density and volume flow for the same operating condition, calculate the corresponding mass rate. Keep the density and flow measurement conditions aligned.
Q&A
Find concise answers to common questions and confusing cases.
No. This calculator takes density, mass flow, and volumetric flow as its three variables. If you have area and average velocity, first calculate Q = area × velocity using consistent units, then use that Q with density.
Yes, when you provide a density that matches the gas conditions represented by the volume-flow value. The calculator does not derive density from pressure or temperature.
The physical rate is the same, but its numeric value depends on the selected unit. Compare both the value and the unit label, such as kg/s versus kg/h.
Notes
Review scope, result limitations, and important precautions before use.
The calculation is only as suitable as its inputs. For gases in particular, density varies with temperature and pressure; use a density corresponding to the same conditions as the volumetric-flow measurement. The calculator does not infer fluid properties, pipe flow, pressure loss, or a standard-volume correction from other measurements.
This is a relationship and unit-conversion aid. It does not replace instrument readings, process engineering, equipment sizing, or a safety review for an operating system.
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