Flow Rate Calculator

Free online Flow Rate Calculator that runs directly in your browser.

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Client-Side Processing

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Instructions

1

Enter data
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2

Click the button
The tool will immediately process your data in the browser.
3

Get the result
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                                                function runTool() {

                                                  return "Result ready in 0.1s";

                                                }

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Flow Rate Calculator – Volume, Mass and Pipe Velocity

Calculate fluid flow rate in water, HVAC, process and industrial systems. Enter pipe diameter, flow rate, density or known units (m³/h, L/min, GPM) and the tool will immediately give youvolume flow Q, mass flow ṁ, velocity vandcross-sectional area A. Built-in unit conversions and examples help you quickly move from measurement data to design parameters.

volume flow Q mass flow ṁ velocity v pipe diameter D cross-sectional area A m³/h L/min GPM kg/s

Run the flow calculator See formulas and examples

What the calculator calculates

Volume flow Qbased on velocity and pipe diameter (or vice versa).
Mass flow ṁafter giving the density ρ of the fluid.
Speed vbased on Q and section A.
Unit conversionsbetween m³/h, m³/s, L/s, L/min, GPM (US), GPH and kg/s, t/h.
Auxiliary results: cross-sectional area A, pipe circumference, volumetric flux at various scales.

The most important relationships

A = π · D² / 4

Q = v · A

ṁ = ρ · Q

D – internal diameter of the pipe, A – cross-sectional area, v – average velocity, Q – volumetric flow, ρ – density.

Units and conversions

Volume flow	Equivalence	Mass flow	Equivalence
1 m³/s	3600 m³/h = 60,000 L/min	1 kg/s	3.6 t/h
1 m³/h	16.667 L/min	ṁ [kg/s]	= ρ [kg/m³] · Q [m³/s]
1 L/s	0.001 m³/s = 3.6 m³/h	1 t/h	≈ 0.2778 kg/s
1 GPM (US)	≈ 3.785 L/min ≈ 0.2271 m³/h	—	—

How to use – step by step

Select the calculation mode: from speed and diameter, from flow and diameter or from flow and speed.
Enter the internal diameter of the pipe (mm or m). The calculator will convert it to meters.
Enter the known velocityvor flowQin any available units.
Optionally, enter the density ρ (e.g. water ~ 998 kg/m³ at 20°C) to obtain the mass flow ṁ.
Read the complete results + convenient conversions.

Calculation examples

1) Flow from velocity and diameter

D = 50 mm ⇒ 0.05 m. v = 1.2 m/s

A = π·D²/4 = 3.1416 · 0.05² / 4 ≈ 0.001963 m²

Q = v A ≈ 1.2 · 0.001963 = 0.002356 m³/s= 2.356 L/s ≈ 8.48 m³/h

If ρ = 998 kg/m³ ⇒ṁ = ρ·Q ≈ 2.35 kg/s