Calculate a reference copper or aluminum AWG wire size from amps, one-way distance, voltage, phase, continuous load, ampacity, and voltage drop.
Calculator
Wire Size Results
Compare ampacity, voltage drop, conductor loss, and nearby AWG sizes.
Ampacity and Load Check
Calculation Details
| Metric | Value | Note |
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Nearby Wire Size Comparison
Pass/fail uses only the selected reference ampacity and entered resistive voltage-drop limit.
| Wire size | Area | Ampacity | Drop | Result |
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AWG wire size calculator for amps and distance
This calculator screens common American Wire Gauge sizes from 14 AWG through 4/0 AWG. It checks reference ampacity and estimated voltage drop independently, then selects the first copper or aluminum size that passes both entered limits. The result includes the approximate metric cross-sectional area, voltage at the load, effective circuit resistance, conductor power loss, and maximum one-way run at the selected drop limit.
Enter the load current that can actually flow, not only the breaker label. Enter one-way distance from source to load in feet or meters; the formula accounts for the return path for DC and single-phase circuits. For balanced three-phase circuits, enter line-to-line voltage.
How the two sizing checks work
Ampacity limits heating under stated installation conditions. Voltage drop limits how much source voltage is lost along the run. A short circuit may be controlled by ampacity, while a long or low-voltage circuit may need a larger conductor even when the smaller size has enough reference ampacity.
planning current = noncontinuous amps + 125% x continuous amps
DC or single phase: voltage drop = 2 x length x load amps x resistance / 1,000
balanced three phase: voltage drop = √3 x length x load amps x resistance / 1,000
Wire-size example
A 24 A load that is entirely continuous produces 30 A of planning current. For a 100 ft, 240 V single-phase copper circuit with a 3% drop target, both reference checks first pass at 10 AWG, approximately 5.26 mm². The output table shows how nearby gauges compare.
AWG and square millimeters
AWG is a North American conductor-size system: a smaller gauge number means a larger conductor. Sizes larger than 1 AWG continue as 1/0, 2/0, 3/0, and 4/0. The displayed mm² value is the nominal conductor area corresponding to the AWG size, not a claim that a metric cable with a nearby area has the same listing, construction, insulation, or permitted ampacity.
Reference ampacity columns
The 60°C and 75°C choices are planning references, not permission to use a temperature column. Terminal temperature ratings, conductor insulation, material, ambient temperature, number of current-carrying conductors, raceway or cable type, wet locations, and equipment-specific rules can change the allowable ampacity. The table also applies conservative small-conductor limits.
Continuous current cannot exceed total load current. The calculator rejects that input instead of silently changing it. It also reports when no conductor through 4/0 in the built-in table passes both checks, rather than presenting the largest listed size as a valid answer.
Voltage drop, power loss, and maximum length
Voltage drop is estimated from reference resistance per 1,000 ft at ordinary conditions. Actual resistance changes with conductor temperature, construction, connections, and AC effects. Power loss is the estimated heat produced in the current-carrying conductors at the entered load. Maximum length is the one-way distance at which the recommended size reaches the selected voltage-drop percentage.
A 3% branch-circuit drop is a common design target, but it is not a universal pass/fail rule for every system. The correct limit depends on the source, feeder and branch-circuit combination, equipment requirements, and applicable rules.
Verify the final conductor selection
Southwire's voltage-drop calculator and building wire selector provide manufacturer tools for more detailed project checks. Final selection remains subject to current codes, product listings, a licensed electrician, and the authority having jurisdiction.
This page does not size service conductors, equipment grounding conductors, raceways, parallel conductors, motors, HVAC equipment, welders, transformers, generators, solar systems, battery cables, or EV charging circuits under their special rules. It does not calculate correction or adjustment factors, fault current, short-circuit protection, neutral loading, harmonics, conduit fill, or terminal compatibility.
Frequently asked questions
Why can distance require a larger wire?
Resistance accumulates with conductor length. A gauge may pass the ampacity check but exceed the entered drop limit over a long run, so the voltage-drop check becomes the controlling constraint.
Should I enter one-way or round-trip distance?
Enter one-way distance from the source to the load. The calculator applies the appropriate circuit factor internally.
Can I use meters?
Yes. Select meters and the calculator converts the entered length to feet for the reference resistance table. Results show both feet and meters.
Does a calculated AWG prove code compliance?
No. It is a transparent planning estimate based on the selected reference column and resistive voltage-drop model. Verify all project conditions and local requirements before installation.
Can the continuous portion be greater than total amps?
No. Continuous load is part of total load. Correct the inputs if the continuous portion exceeds total current.