Flow Rate Calculator
A flow of 100 liters over 20 minutes has a rate of 5 L/min. This flow rate calculator uses the formula flow rate equals volume divided by time to solve for any one of the three values. Enter any two values and the tool calculates the third. Use consistent units for volume and time, such as liters and minutes, or gallons and hours.
Quick answer
Flow rate equals volume divided by time. It measures how much of a substance moves per unit of time.
Enter exactly two positive values and leave the third empty.
What this tells you
- •Flow rate equals volume divided by time. It measures how much of a substance moves per unit of time.
- •Volume equals flow rate times time. Use this to find total volume moved over a period.
- •Time equals volume divided by flow rate. Use this to find how long a task will take.
- •All values must be positive. Time cannot be zero.
- •Units must be consistent. The calculator does not convert between unit systems.
How to Use
- 1Enter the two values you know and leave the third empty.
- 2The calculator solves for the missing value automatically.
- 3Ensure all values use consistent units. Mixing liters with gallons or minutes with hours will give nonsense answers.
How It Works
Formula
flow rate = volume / timeFlow rate is the amount of a substance that passes through a system per unit of time. Divide the total volume by the total time to get the average rate. Rearranged, volume equals rate times time, and time equals volume divided by rate. The calculator uses whichever rearrangement matches the field you left empty.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Find flow rate
Find volume
Find time
Flow Rates for Common Pipes
| Pipe size | Typical flow (L/min) |
|---|---|
| 1/2 inch | 15-25 |
| 3/4 inch | 30-50 |
| 1 inch | 50-80 |
| 2 inch | 150-250 |
Common mistakes
- Mixing unit systems. Volume in gallons and time in minutes gives a different rate number than liters per second.
- Forgetting that flow rate is an average. Real flow rates often vary over time.
- Using zero for time. Division by zero is undefined.
Embed this calculator on your site
Drop this single line where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use with attribution.
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