ELECTRICAL
Estimate a copper or aluminum AWG candidate from voltage, current, one-way distance and a voltage-drop target. Enter your measurements below and the estimate updates instantly.
Voltage-drop sizing only: this result does not check ampacity, breaker size, terminals or NEC/local approval.
Formula, validation and worked example reviewed November 12, 2026. See our calculation methodology.
Enter line-to-line voltage and line current for balanced three phase. This fixed 75°C resistance model omits reactance and power-factor effects.
Smallest listed size meeting this voltage-drop limit; not final wire sizing.
Required area 10,750 cmil · Listed selection 16,510 cmil · Listed range 14 AWG–4/0.
Fixed resistance model at 75°C: K = 12.9 copper / 21.2 aluminum Ω·cmil/ft. No temperature correction.
One-way length; AC assumes unity power factor and neglects reactance. Three phase assumes balanced load, line current and line-to-line voltage.
✓ Instant calculation on your device · Verify code-sensitive work locally
Sizing method and safety
This wire gauge size calculator finds the circular-mil area needed for the selected voltage-drop limit, then moves up to the next conductor size in its limited common-size 14 AWG through 4/0 list, including 3 AWG. It is not a list of every AWG size.
The size of an electrical conductor refers to its cross-sectional area (measured in circular mils (CM) or AWG in the US). The larger the cross-sectional area, the more current the wire can transmit with lower resistance—very similar to water flowing through a wider pipe with less pressure loss. We derive the required conductor area from Ohm's law and conductor resistivity:
where:
For a balanced three-phase AC circuit, three current-carrying phase conductors are used instead of a two-wire loop. The calculator accepts line-to-line voltage and line current, modifying the required area of a single conductor to:
The factor of √3 ≈ 1.732 converts between phase and line quantities in a balanced three-phase system, replacing the factor of 2. The calculator automatically selects the next AWG size up from its listed 14 AWG – 4/0 table so the voltage-drop limit is never exceeded. To check apparent power feeding that circuit, use the kVA to amps calculator.
Allowed volts = system voltage x maximum drop percent / 100Required CM = phase multiplier x K x current x one-way length / allowed voltsSelect the next listed conductor with at least the required circular-mil areaShows circular-mil area alongside base NEC Table 310.16 (60°C & 75°C) ratings and 240.4(D) small-conductor limits. Always verify both ampacity and voltage drop.
| Wire Size | Circular Mils (CM) | Copper 60°C / 75°C Ref | Aluminum 60°C / 75°C Ref |
|---|---|---|---|
| 14 AWG | 4,110 CM | 15 A / 15 A* | Not typically used |
| 12 AWG | 6,530 CM | 20 A / 20 A* | 15 A / 15 A* |
| 10 AWG | 10,380 CM | 30 A / 30 A* | 25 A / 25 A* |
| 8 AWG | 16,510 CM | 40 A / 50 A | 35 A / 40 A |
| 6 AWG | 26,240 CM | 55 A / 65 A | 40 A / 50 A |
| 4 AWG | 41,740 CM | 70 A / 85 A | 55 A / 65 A |
| 2 AWG | 66,360 CM | 95 A / 115 A | 75 A / 90 A |
| 1/0 AWG | 105,600 CM | 125 A / 150 A | 100 A / 120 A |
| 2/0 AWG | 133,100 CM | 145 A / 175 A | 115 A / 135 A |
| 4/0 AWG | 211,600 CM | 195 A / 230 A | 150 A / 180 A |
Enter system voltage, current, one-way distance, conductor material, phase and maximum drop. The tool calculates required circular mils and selects the next listed AWG size.
Under NEC Table 310.16 (75°C terminals), a 50-amp circuit requires 6 AWG copper wire or 4 AWG aluminum wire. If the run exceeds 100 feet at 240V, upsize to 4 AWG copper to limit voltage drop to under 3%.
A 100-amp subpanel typically uses 3 AWG copper wire or 1 AWG aluminum wire for short runs. For distances over 100 feet, 1/0 or 2/0 aluminum wire is standard to control voltage drop.
Under NEC 240.4(D), a 30-amp circuit requires 10 AWG copper wire (or 8 AWG aluminum). For long runs exceeding 85 feet at 240V, upsize to 8 AWG copper to keep voltage drop under 3%.
A long run, high current, low system voltage, or tight drop limit increases the circular-mil area required.
No. It only sizes for the selected voltage-drop limit. Ampacity, derating, terminals, protection, and local code require separate verification.
If the calculated area falls between listed conductors, the smaller one cannot meet the selected drop limit under this formula.
Yes. Select aluminum so the calculation uses the material constant configured for aluminum.
The calculated area exceeds the largest size in this tool. Use a professional design that can consider larger or parallel conductors and the complete installation.
Yes. Enter the actual system voltage, load current and one-way distance. Lower-voltage systems often need larger conductors to hold the same percentage-drop limit.
The calculator uses the balanced three-phase square-root-of-three multiplier with line-to-line voltage, line current and one-way distance, then selects the next listed AWG area that meets the chosen drop limit.
This US-facing calculator reports American Wire Gauge sizes from 14 AWG through 4/0. Metric cable sizing normally uses square millimeters and requires a separate conversion and code check.
Use this electrical cable size calculator when voltage drop is the sizing question. It selects the next listed AWG conductor that meets the entered drop limit, but it does not replace an ampacity or code calculation.
Low-voltage runs can lose a meaningful share of supply voltage over distance. Enter the real one-way length and current instead of choosing a gauge by habit.
Select DC / single phase, choose copper or aluminum, and set the maximum drop used for the estimate. Verify ampacity and protection separately.
Select three phase to use the square-root-of-three sizing formula. A complete commercial design may also need load balance, power factor and installation conditions.
Current is one voltage-drop input, but it does not establish ampacity by itself. Check load rules, ampacity, terminals and protection separately.
For a 50A 240V circuit (range or Level 2 EV charger), standard 75°C copper requires 6 AWG (or 4 AWG aluminum). Over 100 feet, step up to 4 AWG copper to keep voltage drop under 3%.
A 100A 240V subpanel requires 3 AWG copper or 1 AWG aluminum at standard 75°C ratings. Over long distances (>100 ft), 1/0 or 2/0 aluminum is commonly used to prevent voltage loss.
A 30A 240V circuit requires 10 AWG copper under NEC 240.4(D). For long runs exceeding 85 feet, upsize to 8 AWG copper to stay within the recommended 3% drop limit.
The result moves to the next listed common size from 14 AWG through 4/0. An above-range result is a warning to obtain a professional design, not a conductor recommendation.
Method references: Southwire Voltage Drop Calculator · Southwire Building Wire Selector guidance