The Wire Size Calculator sizes a conductor from the load current, one-way run distance, system voltage, material and the maximum allowed voltage drop. It checks both ampacity and voltage drop and returns the smallest AWG or kcmil that satisfies both.
Wire Size Calculator (Amps + Distance)
Find the correct wire size for a load based on amperage, one-way distance, voltage, material and allowed voltage drop. Covers copper and aluminum, single and three phase.
Inputs
Result
--
recommended size
--
voltage drop
About Wire Size Calculator (Amps + Distance)
Features
- Sizes by amps + distance
- Single or three phase
- Copper or aluminum
- Tunable allowed voltage drop (default 3%)
- Reports resulting drop, ampacity and limiting factor
How to Use
- Enter load current, one-way distance and system voltage.
- Pick phase, material and allowed drop.
- Read the recommended size and the resulting drop.
Examples
Example: 50 A, 100 ft, 240 V, single phase, copper, 3% drop -> recommends 6 AWG (drop ~2.9%, 65 A).
Benefits
- Avoids undersized wires that overheat or sag voltage
- Fast sizing for feeders and branch circuits
Frequently Asked Questions
What does this calculator do?
It finds the smallest standard wire that both carries the load current and keeps voltage drop within your chosen limit over the run length.
How much voltage drop is allowed?
NEC recommends no more than 3% drop for branch circuits and 5% total for the whole circuit. Use 3% for best results.
Does phase matter?
Yes. Three-phase runs have about 87% of the single-phase drop for the same wire, because only sqrt(3) factor applies.
Copper or aluminum?
Aluminum needs a larger size for the same current. The tool picks the right size for whichever material you choose.
Is my data saved?
No. All math runs in your browser.