Formula used
The calculator first determines load current from amperes, watts, kilowatts, or kilovolt-amperes. It then applies continuous-load, future-growth, and safety multipliers. The final design current is used for conductor selection.
Conductor resistance is calculated from resistivity, length, and effective cross-sectional area. Operating temperature adjusts resistivity through the material temperature coefficient. Parallel conductors increase effective area and reduce calculated resistance.
R = ρL ÷ A
Basic DC and single-phase circuits use twice the one-way conductor length. Balanced three-phase circuits use the square root of three multiplier. AC calculations combine resistance and reactance using the entered power factor.
Single-phase: Vd = 2 × I × L × (R cos φ + X sin φ)
Three-phase: Vd = √3 × I × L × (R cos φ + X sin φ)
Voltage-drop percentage = Vd ÷ source voltage × 100
How to use this calculator
- Select a preset or enter the system voltage manually.
- Choose DC, single-phase, split-phase, or three-phase operation.
- Enter current directly or calculate it from electrical power.
- Enter the one-way conductor length and its measurement unit.
- Select an AWG, kcmil, or custom conductor area.
- Choose conductor material, temperature, installation method, and parallel count.
- Set the allowable voltage-drop percentage and ampacity conditions.
- Enable motor starting or multiple segments when required.
- Press the calculate button and review every design check.
Electrical design guidance
AWG and conductor area
American Wire Gauge identifies round conductor sizes using an inverse numbering system. Smaller gauge numbers represent larger conductor areas. Large power conductors are often identified using kcmil values.
Voltage drop versus ampacity
Voltage-drop sizing limits lost voltage across the conductor run. Ampacity sizing limits conductor heating under expected installation conditions. The larger conductor required by either check should normally govern.
Copper and aluminum
Copper provides lower resistance for the same cross-sectional area. Aluminum usually requires a larger conductor for equal voltage-drop performance. Connections must also match the conductor material and equipment rating.
One-way and round-trip length
Enter only the one-way distance between source and load. Two-wire calculations apply the return-path multiplier automatically. Three-phase calculations apply the balanced phase multiplier automatically.
Temperature and installation
Conductor resistance rises as operating temperature increases. Bundling and high ambient temperatures can reduce available ampacity. Raceway, tray, burial, and free-air installations require separate verification.
Engineering limitations
This calculator supports preliminary design and conductor comparisons. It does not replace local codes or detailed protective-device coordination. A qualified professional should approve critical or high-energy installations.
Saved calculation history
Saved entries remain inside this browser only.