Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Flow rate (gal/min)
12.24
Gallons per hour
734
Liters per minute
46.3
Minutes to fill volume
40.9
Pipe area (sq in)
0.785
Cubic feet per second
0.0273
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter inside diameter (in).
- 2Enter flow velocity (ft/s).
- 3Enter volume to fill (gal).
- 4Read your flow rate (gal/min) on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Keep water velocity under about 7 ft/s in copper to avoid erosion and noise. Doubling pipe diameter roughly quadruples capacity at the same velocity.
Worked example
Using the values the calculator loads with:
Inputs
- Inside diameter: 1 in
- Flow velocity: 5 ft/s
- Volume to fill: 500 gal
Results
- Flow rate (gal/min): 12.24
- Gallons per hour: 734
- Liters per minute: 46.3
- Minutes to fill volume: 40.9
- Pipe area (sq in): 0.785
- Cubic feet per second: 0.0273
What each field means
Inputs
- Inside diameter (in)
- The inside diameter used in the calculation, measured in in. Starts at 1 in so you have a working example on load.
- Flow velocity (ft/s)
- The flow velocity used in the calculation, measured in ft/s. Starts at 5 ft/s so you have a working example on load. Accepted range: 0.1–20 ft/s.
- Volume to fill (gal)
- The volume to fill used in the calculation, measured in gal. Starts at 500 gal so you have a working example on load.
Results
- Flow rate (gal/min)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Gallons per hour
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Liters per minute
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Minutes to fill volume
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Pipe area (sq in)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cubic feet per second
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the pipe flow rate & velocity calculator work?
Keep water velocity under about 7 ft/s in copper to avoid erosion and noise. Doubling pipe diameter roughly quadruples capacity at the same velocity. The underlying maths is: GPM = area (sq ft) × velocity (ft/s) × 448.8.
What do I need to enter?
3 values: inside diameter, flow velocity, and volume to fill. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the flow rate (gal/min) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Pipe Flow Rate Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/pipe-flow-rate
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/pipe-flow-rate" target="_blank" rel="noopener">Pipe Flow Rate Calculator — RevenueLab</a> (2026).</p>
Source: [Pipe Flow Rate Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/pipe-flow-rate) (2026).