Know your wire size and voltage drop before you run the circuit
Enter your current, distance and voltage and get a real result — voltage drop in volts and percent, or a recommended AWG wire size — with the formula and assumptions shown, not just a bare number.
Choose your calculator
Both are free, need no login, and show the formula behind the result.
Voltage Drop Calculator
Voltage drop in volts and percent, voltage at the load, and an ampacity check — for a wire size, current, distance and voltage you already have.
Open calculator →Wire Size Calculator
A recommended AWG wire size from your current, distance and voltage — checked against both NEC ampacity and a voltage drop target.
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How these electrical calculators work
Enter your circuit details
Current, one-way distance, voltage and conductor material — no sign-up required.
Get your result
The computed value, the formula behind it, and the standard tables the assumptions are drawn from — shown, not hidden.
Confirm before you wire it
Use the result to plan, then confirm final sizing with a licensed electrician or your local code.
Why not just use a generic calculator?
Most voltage drop and wire size tools stop at a single number and hide the math. These tools show the formula and the NEC tables behind every result, check ampacity alongside voltage drop rather than voltage drop alone, and support DC and three-phase circuits and both copper and aluminum — not just a generic 120V single-phase case.
What this isn't
These calculators are not engineering advice, a code compliance check, or a substitute for a licensed electrician. They estimate from standard published resistance and ampacity tables and don't account for ambient temperature, conduit fill or bundled-conductor derating. Use them to plan — then confirm final sizing against your local code.
Frequently asked questions
Is Electrical Workbench really free?
Yes. Every calculator result — the value, the formula and the assumptions behind it — is free with no account or login required.
Are these calculators a substitute for a licensed electrician?
No. They estimate voltage drop and wire size from standard published tables for planning purposes. They are not engineering advice, a code compliance check or a substitute for a licensed electrician's review.
Do the calculators cover DC and three-phase circuits?
Yes — both tools support single-phase, DC and three-phase circuits, and copper or aluminum conductors.