Wire Gauge & Voltage Drop Calculator
Calculate the proper wire gauge for electrical circuits. Determine minimum wire size based on current, distance, and acceptable voltage drop to meet NEC requirements.
Circuit Details
Distance from panel to load
Better conductivity, higher cost
NEC recommends 3% for branch circuits
Voltage Drop Basics
Voltage drop occurs as current flows through wire resistance. Excessive drop causes dimming lights, motor overheating, and equipment malfunction.
- • NEC recommends max 3% for branch circuits
- • Total drop (feeder + branch) should be under 5%
- • Copper conducts better than aluminum
How to Use
- Select your system voltage (120V, 240V, etc.)
- Enter the expected load current in amps
- Measure the one-way distance from panel to load
- Choose copper or aluminum conductor
- Click Calculate to see the minimum wire gauge
FAQ
Why does voltage drop matter?
Excessive voltage drop causes lights to dim, motors to run hot and inefficiently, and sensitive electronics to malfunction. It also wastes energy as heat in the wire.
What's the difference between copper and aluminum?
Copper has about 60% better conductivity than aluminum, so you need larger aluminum wire for the same current. Aluminum is cheaper and lighter, making it common for large feeders. Copper is standard for branch circuits.
Does this account for ampacity limits?
This calculator focuses on voltage drop. You must also verify the wire meets NEC ampacity requirements (Table 310.16) for your current and installation conditions. The larger of the two requirements determines your minimum wire size.