Enter the circuit voltage, current, one-way distance, conductor material and a maximum voltage drop, and see the voltage drop for each common AWG size with the smallest size meeting the target highlighted.
Important: This tool covers voltage-drop maths only. Ampacity limits and code requirements, such as NEC tables, also govern wire size and are not covered here. Verify any installation with a licensed electrician and local code.
Voltage drop is current multiplied by the resistance of the full round trip: the conductor resistance per 1000 ft for each AWG size, multiplied by twice the one-way distance divided by 1000. Aluminium resistance is taken as about 1.64 times the copper figure for the same gauge. The table shows the drop for each common size as volts and as a percentage of the circuit voltage, and highlights the smallest conductor that meets the drop target entered, by voltage drop alone. That qualification matters: this tool covers voltage-drop maths only, and ampacity limits and code requirements, such as NEC tables, also govern wire size and are not covered here. A size that satisfies voltage drop can still be too small for the current it carries, so verify any installation with a licensed electrician and local code.
Does the smallest size meeting the voltage drop target mean that size is safe to use? No. This tool covers voltage-drop maths only. Ampacity limits and code requirements, such as NEC tables, also govern wire size and are not covered here, so a size that passes on voltage drop may still be undersized for the current. Verify any installation with a licensed electrician and local code.
Why is the round-trip distance used? Current travels out on one conductor and back on the other, so the total wire length in the circuit is twice the one-way distance. Voltage is lost along both legs, and the drop calculation has to include both.
Why does aluminium need a larger gauge than copper? Aluminium has roughly 1.64 times the resistance of copper for the same size, so over the same run it drops more voltage. Matching a copper voltage drop in aluminium generally means going about two AWG sizes larger, subject to the ampacity and code checks this tool does not cover.