Calculator tool
How this calculator works
Use the explanation to understand the formula, assumptions, and practical limits behind the calculator result.
What This Calculator Does
This calculator estimates voltage drop for a copper conductor from current, wire length, wire gauge, and source voltage. For a single-phase circuit it uses the round-trip conductor path:
where is one-way length, is current, and is conductor resistance per unit length.
How to Read the Result
The percentage drop matters because equipment sees the delivered voltage, not only the source voltage. Electrical guidance commonly treats about 3% branch-circuit drop as a useful design target, but the actual acceptable limit depends on the installation, local code, load type, temperature, conductor material, and professional design requirements.
Use the calculator for planning, then verify conductor tables, code requirements, and field conditions before finalizing a circuit.
Frequently asked questions
Why does the formula use twice the wire length?
Because current travels out and back through the circuit. The calculator asks for one-way length, then doubles it to estimate the full conductor path.
Does wire gauge matter more than length?
Both matter. Longer runs increase resistance, while larger conductors lower resistance. Changing either one can materially change the voltage drop.
Is 3% always a legal limit?
No. It is a common design guideline, not a universal rule for every installation. Final design still depends on the applicable code and equipment requirements.
What can make the real drop differ from the estimate?
Temperature, conductor material, splice quality, load variation, and actual installed length can all change the real result.
