Trade utility
Wire Size Calculator
Estimate a copper wire size from load current, run length, supply voltage, and a target voltage-drop limit.
Interactive calculator
Estimate copper wire size from load and run length
Use load current, supply voltage, one-way run length, and a target voltage-drop limit to estimate a copper wire size for planning. This is a planning tool, not a substitute for local electrical code review.
Results
Recommended wire
10 AWG
5.26 mm2 copper
Estimated voltage drop
5.75 V
2.4%
Estimated load voltage
234.25 V
240 ft total conductor length
Ampacity reference
30 A
Planning estimate uses conservative common copper branch-circuit reference values.
How to use it
- 01Enter the load current, supply voltage, and one-way run length.
- 02Choose the maximum voltage-drop target you want to stay within.
- 03Review the recommended copper wire size and the estimated voltage drop at that size.
Result guide
- This page is a planning estimator and does not replace local code review or installation-specific design.
- The calculation assumes a simple copper circuit and doubles the one-way run to account for the full conductor path.
- Ambient temperature, conduit fill, insulation type, and code rules can require a different final conductor size.
About this calculator
Wire-size planning often starts with two constraints: carrying the load current safely and keeping voltage drop within a practical limit over the full run length.
A useful planning page should therefore check both current capacity and voltage-drop behavior instead of sizing conductors from amps alone.
Frequently asked questions
Why can a long run require a larger wire even when amps stay the same?
Because conductor resistance increases with length, which increases voltage drop and can force a larger wire than ampacity alone would suggest.
Why is this only a planning tool?
Because final electrical sizing also depends on code rules, termination ratings, temperature correction, bundling, and installation details.
Why does the calculator use the full conductor length?
Because current travels out and back, so voltage-drop planning needs the total conductor path rather than only the one-way distance.
Reviewed by Dr. Elena Rostova, MD, PhD
Medical Doctor & Clinical Nutrition Researcher
Reviews health index calculators, unit converter benchmarks, and mathematical models against WHO guidelines and peer-reviewed research.
Sources: Per WHO guidelines / Peer-reviewed research/Standard estimating formulas for area, volume, and material counts/Common trade calculation references for unit assumptions
Disclaimer: Calculator results are for general reference and educational purposes only per WHO standards. Health indexes and mathematical models are not a substitute for professional medical diagnosis, clinical nutrition, or certified trade advice.
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