Use this free wire size calculator to estimate copper AWG size, voltage drop, percent drop, and load voltage from amps, length, source voltage, phase, and a drop limit.
15 A over 75 ft
This is not a code-complete wire sizing tool. Ampacity, insulation rating, terminals, raceway, temperature, material, and local code must be checked separately.
Recent wire size estimates will appear here.
Wire-size estimates are browser-only planning math. Code-compliant electrical design needs qualified review.
Inputs and recent answers stay in this browser tab and are not sent to a server.
Estimate copper AWG size for a voltage-drop target.
Compare branch-circuit and longer-run examples.
See estimated voltage drop and load voltage together.
Learn why current and length affect conductor choice.
Check low-voltage DC runs where percent drop is sensitive.
Compare single/DC and balanced three-phase voltage-drop assumptions.
12 AWG; 3.573 V drop, 2.9775% drop, 116.427 V load
10 AWG; 5.994 V drop, 2.4975% drop, 234.006 V load
10 AWG; 5.1909562703 V drop, 2.495652053% drop, 202.80904373 V load
12 AWG; 0.6352 V drop, 2.6466666667% drop, 23.3648 V load
10 AWG; 3.5964 V drop, 2.997% drop, 116.4036 V load
6 AWG; 1.26432 V drop, 2.634% drop, 46.73568 V load
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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 copper AWG size for a voltage-drop target. Compare branch-circuit and longer-run examples. It works best when you already know the measurements, amounts, units, or options the page asks for.
In plain language: The calculator tests common copper AWG sizes from 14 AWG through 4/0 and returns the first size whose estimated voltage drop is within the selected percentage. Single/DC uses the out-and-back path; balanced three-phase uses the square-root-of-3 factor. The examples on the page are there so you can compare your inputs with a worked example before copying the answer.
Source voltage: the voltage at the supply side before the wire run loses voltage. Current amps: the expected load current used for the voltage-drop estimate. One-way length: the source-to-load distance in feet, not the full out-and-back loop length. Max voltage drop: the percentage limit the calculator tries to stay under, such as 3%. Circuit type: single/DC uses an out-and-back factor of 2; balanced three-phase uses sqrt(3).
Read the headline answer, 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 voltage-drop planning math for copper conductors only. It does not approve wire size or check ampacity, breaker size, insulation rating, terminals, raceway fill, temperature correction, aluminum conductors, equipment instructions, or local electrical code. Also check the unit, scale, mode, and result limit because small input changes can change the answer.
No. This estimates voltage drop only. Real wire sizing also needs ampacity, conductor insulation, raceway fill, terminals, temperature, material, and local code rules.
Longer wire has more resistance. More resistance causes more voltage drop, so increasing wire size can reduce the estimated voltage lost along the run.
Enter the physical distance from the source to the load. The calculator applies the circuit factor internally, so do not double the length for a simple single-phase or DC run.
The same volt loss is a bigger percentage of a 12 V, 24 V, or 48 V system than it is of a 120 V or 240 V system. That can push the estimate toward a larger copper AWG size.
No. This version uses approximate copper AWG resistance values only. Aluminum conductors, hot conductors, conduit fill, and AC impedance can change the real result.
The run may need a shorter length, lower current, higher source voltage, a larger conductor than this simple list supports, or a qualified design review.
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.