Wire Voltage Drop Calculator
Voltage drop over a wire run by length and gauge.
Enter your values
Enter the one-way length in ft.
Enter the current in A.
Enter the resistance per 1000 ft in ohms (12 AWG copper default).
Enter the supply voltage in V.
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.
- Voltage drop
- 3.14 V
- Percent drop
- 2.62%
- Voltage at load
- 116.86 V
- Status
- Within recommended 3% limit
Quick answer
Voltage drop = 2 x length x current x resistance per foot (for round-trip circuits).
Vdrop = 2 L I R_per_ft
At a glance
| What it does | Voltage drop over a wire run by length and gauge. |
|---|---|
| Category | Engineering |
| Inputs needed | One-way length, Current, Resistance per 1000 ft, Supply voltage |
| Main output | Voltage drop |
| Formula | Vdrop = 2 L I R_per_ft |
| Cost | Free — no sign-up, no download |
How to use the Wire Voltage Drop Calculator
- 1Enter the one-way wire length, load current and the wire's resistance per 1000 ft (from an ampacity table).
- 2Enter the supply voltage.
- 3Check the percent drop against the common 3% design guideline.
Inputs explained
- One-way length(ft)
- Enter the one-way length in ft.
- Current(A)
- Enter the current in A.
- Resistance per 1000 ft(ohms (12 AWG copper default))
- Enter the resistance per 1000 ft in ohms (12 AWG copper default).
- Supply voltage(V)
- Enter the supply voltage in V.
Worked example
Using the values the calculator loads with:
Inputs
- One-way length50 ft
- Current10 A
- Resistance per 1000 ft3.14 ohms (12 AWG copper default)
- Supply voltage120 V
Results
- Voltage drop3.14 V
- Percent drop2.62%
- Voltage at load116.86 V
- StatusWithin recommended 3% limit
Frequently asked questions
Why multiply length by 2?
Current travels out and back through the circuit, so both conductors contribute resistance.
What if drop is too high?
Use a thicker (lower AWG number) wire or shorten the run to bring the drop back under 3%.
What do I need to enter into the Wire Voltage Drop Calculator?
Just 4 values: one-way length, current, resistance per 1000 ft, supply voltage. 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 Voltage Drop Calculator work out the answer?
Voltage drop = 2 x length x current x resistance per foot (for round-trip circuits). It applies the formula Vdrop = 2 L I R_per_ft and shows the working so you can check each step by hand.
Is the Wire Voltage Drop 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.