Wire Gauge Calculator
Cable size for current, length and voltage drop.
Enter your values
Enter the current in A.
Enter the one-way run length in m.
Enter the system voltage in V.
Enter the allowed voltage drop in %.
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 gauge
- 10 AWG
- Actual voltage drop
- 3.28 V (2.73%)
- Maximum allowed drop
- 3.6 V
- Power lost in the cable
- 65.6 W
- Note
- Always confirm against local electrical code ampacity tables.
Quick answer
Choose a wire gauge whose resistance keeps voltage drop under 3% for the current and one-way run length.
Vdrop = 2 × I × L × R_per_metre
At a glance
| What it does | Cable size for current, length and voltage drop. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Current, One-way run length, System voltage, Allowed voltage drop |
| Main output | Recommended gauge |
| Formula | Vdrop = 2 × I × L × R_per_metre |
| Cost | Free — no sign-up, no download |
How to use the Wire Gauge Calculator
- 1Enter the load current in amps.
- 2Enter the one-way cable run length.
- 3Set the acceptable voltage drop, usually 3%.
Inputs explained
- Current(A)
- Enter the current in A.
- One-way run length(m)
- Enter the one-way run length in m.
- System voltage(V)
- Enter the system voltage in V.
- Allowed voltage drop(%)
- Enter the allowed voltage drop in %.
Worked example
Using the values the calculator loads with:
Inputs
- Current20 A
- One-way run length25 m
- System voltage120 V
- Allowed voltage drop3 %
Results
- Recommended gauge10 AWG
- Actual voltage drop3.28 V (2.73%)
- Maximum allowed drop3.6 V
- Power lost in the cable65.6 W
- NoteAlways confirm against local electrical code ampacity tables.
Frequently asked questions
Why 3% voltage drop?
It's the widely used design limit for branch circuits; more than that wastes energy and dims or overheats loads.
Does length really matter?
Yes — drop is proportional to run length, so long runs often need a gauge or two thicker than ampacity alone suggests.
What do I need to enter into the Wire Gauge Calculator?
Just 4 values: current, one-way run length, system voltage, allowed voltage drop. 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 Wire Gauge Calculator work out the answer?
Choose a wire gauge whose resistance keeps voltage drop under 3% for the current and one-way run length. It applies the formula Vdrop = 2 × I × L × R_per_metre and shows the working so you can check each step by hand.
Is the Wire Gauge 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.