Use this free wire resistance calculator to estimate total ohms for common copper AWG wire sizes and lengths.
12 AWG copper, 100 ft
This is a simplified copper resistance estimate. Temperature, strand type, material, connections, and code rules can change real behavior.
Estimate loop resistance for common copper AWG sizes.
Compare how thicker wire lowers resistance.
Prepare a resistance value for voltage-drop thinking.
Learn why length matters in electrical runs.
About 0.3176 ohms
Resistance estimate
One-way resistance estimate
Plain-language answers about when to use the tool, what it does with your inputs, what to double-check, and how privacy works.
Use it when your task matches one of these common needs: Estimate loop resistance for common copper AWG sizes. Compare how thicker wire lowers resistance. It works best when you already know the values, dates, units, or settings the page asks for.
In plain language: The calculator scales the copper ohms-per-1,000-feet value by wire length and multiplies by the number of conductor lengths included. The examples on the page are there so you can compare your inputs with a filled-out calculation before copying the answer.
Copper wire size: AWG size used to look up approximate resistance. One-way length: the conductor length in feet before multiplying by conductor count. Conductor count: how many conductor lengths are included in the total resistance.
Read the main answer first, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
This is a simplified copper resistance estimate. Temperature, strand type, material, connections, and code rules can change real behavior. Also check that you used the right unit, date, scale, or mode because small input changes can change the result.
A simple circuit usually has an out path and a return path. If each path is the same length, using conductor count 2 estimates the loop resistance.
Yes. Copper resistance changes with temperature, and real installations also involve terminations, material, raceway, and code rules. This tool keeps the estimate simple.
No. The calculator runs in your browser tab. Your recent answers stay only on the page while you use it, and they are not sent to a server.