Part of the DIY & Home collection — 4 tools available
Wire Gauge & Length Calculator
Calculate the correct wire gauge for your circuit based on amperage, voltage, and distance. Prevent voltage drop and ensure safe electrical wiring.
About This Calculator
Using the wrong wire gauge for an electrical circuit causes voltage drop, overheating at connections, and potential fire hazards that can destroy property and endanger lives. Voltage drop increases with both distance and amperage — a 20-amp circuit running 100 feet needs significantly heavier wire than the same circuit at 25 feet because resistance accumulates over distance. The National Electrical Code requires keeping voltage drop under 3% for branch circuits. Our wire gauge calculator determines the minimum AWG wire size based on your circuit amperage, one-way distance, and maximum acceptable voltage drop.
The Formula Behind This Calculator
Voltage drop = 2 * Length * Current * Resistance / 1000 Use thicker wire for longer runs
Understanding the math helps you verify results and make better decisions for your project.
How to Use
- 1Enter the circuit amperage (breaker rating or expected load).
- 2Set the circuit voltage (120V standard, 240V for heavy appliances).
- 3Enter the one-way wire length from panel to load.
- 4Set the maximum acceptable voltage drop (3% is the NEC recommendation).
When to Use
- →Running a new circuit to a shed, garage, or outbuilding.
- →Checking if existing wiring is adequate for a new appliance.
- →Planning a solar panel or battery bank wiring run.
Tips
- ✓NEC recommends maximum 3% voltage drop for branch circuits and 5% for feeders.
- ✓When in doubt, go one size larger — slightly thicker wire runs cooler and more efficiently.
- ✓For 240V circuits (dryers, ranges, EV chargers), always use dedicated circuits with proper gauge wire.
FAQ
What happens if I use wire that is too thin?
Undersized wire causes excessive voltage drop (appliances underperform), overheating (fire risk), and breaker tripping. The NEC specifies minimum wire sizes — these are code requirements, not suggestions.
What is voltage drop?
Voltage drop is the reduction in voltage as electricity travels through wire resistance. Longer runs and higher amperage cause more drop. At 3% drop on a 120V circuit, your device receives only 116.4V.
Does wire material matter?
Yes. Copper is the standard. Aluminum wire has about 1.6x more resistance than copper, requiring a larger gauge for the same application. Aluminum is used mainly for service entrance cables.
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