Use electrical standards for real installations
This calculator is a simplified planning estimate. Real electrical work depends on conductor material, temperature, conduit, phase, load type, local code and safety requirements.
Example
With 20 A, 100 units of one-way distance, resistance of 1.588 per 1000 units and a 120 V system, the estimated drop is 2 x 100 x 20 x 1.588 / 1000 = 6.352 V, or about 5.3% of 120 V.
Common mistakes
Use one-way distance if the formula already doubles for round-trip conductor length. Also confirm that the resistance value matches the conductor material, size and unit system you are using.
Limitations
This page is not an electrical design approval. For real wiring, follow local electrical code and have qualified electrical work reviewed by a licensed professional where required.
Last reviewed: 2026-05-17