Voltage Drop Percent Calculator
Estimate voltage lost along a two-conductor run.
Calculate voltage drop percent calculator from clear inputs
Voltage Drop Percent Calculator gives a focused worksheet for home & diy questions where a quick deterministic estimate is more useful than a spreadsheet. The voltage drop percent calculator fields mirror the variables in its formula, and the output separates the main result from supporting values so you can sanity-check this calculation before reusing it.
20 amps over 75 feet at 1.24 ohms per 1000 feet drops 3.72 volts, or 3.1 percent.
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For Voltage Drop Percent Calculator, every calculation runs in your browser with no upload, account, cookie, live lookup, or server-side storage. The voltage drop percent calculator result is best treated as a planning number because the real-world constraints behind this estimate can change the answer. Adjust the voltage drop percent calculator assumptions and confirm important decisions against the relevant source of truth for that exact situation.
Frequently Asked Questions
Why is the wire length doubled?
Current flows out and back, so the circuit's resistance covers both conductors. 20 amps over a 75 ft one-way run at 1.24 ohms per 1,000 ft drops 3.72 volts, 3.1% of 120 V.
What voltage drop is acceptable?
The NEC's informational notes suggest no more than 3% on a branch circuit and 5% total from service to load. Larger drops waste power and can make motors run hot.
Where do I find ohms per 1,000 feet?
In wire tables such as NEC Chapter 9, Table 8. For uncoated copper, 12 AWG is about 2.0 ohms and 10 AWG about 1.24 ohms per 1,000 ft.
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