Copper Pipe Size Calculator
Copper pipe size for water flow demand.
Enter your values
Enter the design flow in GPM.
Enter the max velocity in ft/s.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Recommended copper size
- 1 in
- Minimum ID needed
- 0.825 in
- Velocity at selected size
- 3.88 ft/s
Quick answer
Copper pipe size is chosen so velocity stays around 4-8 ft/s using the pipe's actual inside diameter.
velocity = GPM x 0.408 / ID^2 (in), solved for pipe ID
At a glance
| What it does | Copper pipe size for water flow demand. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Design flow, Max velocity |
| Main output | Recommended copper size |
| Formula | velocity = GPM x 0.408 / ID^2 (in), solved for pipe ID |
| Cost | Free — no sign-up, no download |
How to use the Copper Pipe Size Calculator
- 1Estimate the design flow rate for the pipe run in GPM.
- 2Use 4-6 ft/s for a quiet residential system, up to 8 ft/s for short branch runs.
- 3Pick the smallest type L copper size that keeps velocity under your limit.
Inputs explained
- Design flow(GPM)
- Enter the design flow in GPM.
- Max velocity(ft/s)
- Enter the max velocity in ft/s.
Worked example
Using the values the calculator loads with:
Inputs
- Design flow10 GPM
- Max velocity6 ft/s
Results
- Recommended copper size1 in
- Minimum ID needed0.825 in
- Velocity at selected size3.88 ft/s
Frequently asked questions
Type L or type M copper?
Type L is the common choice for water supply due to its thicker wall and higher pressure rating.
Is copper better than PEX?
Copper is more rigid and rated for higher temperatures, while PEX is cheaper and easier to install — see the PEX pipe size calculator.
What do I need to enter into the Copper Pipe Size Calculator?
Just 2 values: design flow, max velocity. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Copper Pipe Size Calculator work out the answer?
Copper pipe size is chosen so velocity stays around 4-8 ft/s using the pipe's actual inside diameter. It applies the formula velocity = GPM x 0.408 / ID^2 (in), solved for pipe ID and shows the working so you can check each step by hand.
Is the Copper Pipe Size Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.