Voltage Drop Calculator
Estimate voltage drop along a cable run.
Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.
Voltage Drop Calculator
How to use this tool
- Enter the values in the fields above.
- Press Generate to see the result.
- Use Load sample to try the worked example, Copy result to copy it, or Clear to start again.
Worked example
At 10 A through a 50-metre run of cable at 1 ohm per km, drop is 2 × 10 × 1 × 0.05 = 1.00 V, which is 1.00 / 230 × 100 = 0.43% of a 230 V supply.
What this tool does not do / Limits
This is an estimate assuming the stated resistance, a single-phase out-and-back run, and steady current. It is not a substitute for a datasheet, wiring rules, or a qualified electrician, and it ignores temperature rise and reactance.
Frequently asked questions
Why multiply by 2?
Current travels out along one conductor and back along the other, so the run length counts twice.
What drop is acceptable?
Limits depend on local wiring rules and the equipment; this tool only reports the percentage, it does not approve an installation.
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