THE NUMORIX GUIDE
How to use the Fluid Flow Calculator
Last reviewed September 14, 2026
What this calculator does
The area-and-velocity mode uses the continuity relation Q = A v.
Formula and method
The area-and-velocity mode uses the continuity relation Q = A v. The volume-and-time mode uses the average flow definition Q = V/t. The engine converts cubic meters per second to liters per minute by multiplying by 60,000.
Variables and inputs
In area mode, enter cross-sectional area A in m^2 and average velocity v in m/s. In volume mode, enter volume V in m^3 and time t in seconds; the defaults are A = 0.01, v = 2, V = 0.12, and t = 30.
Worked example
For A = 0.01 m^2 and v = 2 m/s: Q = 0.01(2) = 0.02 m^3/s = 1,200 L/min. In volume mode, V = 0.12 m^3 over 30 s gives Q = 0.004 m^3/s = 240 L/min.
How to interpret the result
Volumetric flow rate tells how much fluid volume crosses a section per unit time. The area mode uses an average velocity over a cross-section; the volume mode reports an average over the entered time interval.
Common mistakes to avoid
Use cross-sectional area, not pipe diameter, and convert liters to cubic meters before using Q = V/t. Keep time in seconds so the conversion to L/min remains Q multiplied by 60,000.
Assumptions and limitations
The area model assumes the entered area and average velocity describe the same section and does not calculate pressure loss, viscosity, turbulence, compressibility, or a velocity profile. Volume mode requires positive time and nonnegative volume; area mode itself has no physical-range validation.
Practical use and checks
The Fluid Flow Calculator estimates volumetric flow either from cross-sectional area and average velocity or from a measured volume and elapsed time. In area mode, enter A = 0.01 m^2 and v = 2 m/s as a check; flow should be 0.02 m^3/s, or 1,200 liters per minute. In volume mode, enter 0.12 m^3 over 30 seconds; the average should be 0.004 m^3/s, or 240 L/min. Choose the mode that matches the measurement rather than mixing an area from one pipe with a velocity from another. Use cross-sectional area, not diameter, in Q = A*v. For a circular pipe, calculate area as pi*r^2 first, and keep cubic meters, seconds, and liters consistent. The result is a volumetric rate, not mass flow; density is needed for kg/s. The calculator assumes the entered velocity is an appropriate cross-sectional average and does not model pressure loss, viscosity, turbulence, compressibility, a changing level, leaks, or a velocity profile. Area and velocity with inconsistent units can produce a precise but wrong number, while a zero time makes volume-over-time undefined. For pump or pipe selection, pair the flow estimate with head, friction, temperature, pipe geometry, and the required operating range.