U.S. Electrical and HVAC Calculators

Voltage drop calculator

This calculator estimates the voltage drop on a copper or aluminum run in the United States. Enter the one-way length — the path the cable actually takes. Do not multiply that length by 2. The formula already accounts for the outgoing and return path.

Source voltage
Circuit
Conductor
Voltage-drop target

How the voltage drop calculator works

Results from these calculators are for learning and estimation only. They are not a substitute for a licensed electrician, a licensed HVAC contractor, the local codebook, or manufacturer instructions. The electrical tools use a DC-resistance method and do not calculate ampacity, derating, conduit fill, reactance, or power factor. The BTU tool is only for U.S. room window air conditioners, not central systems, and does not replace a professional load calculation. The methods are written for U.S. practice and are not directly applicable outside the United States. If you use these results, you do so at your own risk.