What Is a Wire Size Calculator?
A wire size calculator estimates the conductor size needed to carry an electrical load while keeping voltage loss within the selected limit. It provides results in American Wire Gauge and square millimeters so that users can compare common imperial and metric cable sizes.
The correct conductor is not always the smallest cable capable of carrying the load. Long cable runs can experience excessive voltage drop, making it necessary to select a larger wire even when the current is relatively low.
Compares the estimated operating current with a simplified conductor current-capacity table.
Estimates the voltage lost across the complete conductor path using cable length and material resistance.
Supports copper and aluminum conductors, along with AWG and metric cross-sectional area results.
How to Use the Wire Size Calculator
- Select whether you want to enter the electrical load in amperes or watts.
- Enter the system voltage and choose DC, single-phase AC or three-phase AC.
- Enter the one-way cable distance and select meters or feet.
- Choose copper or aluminum as the conductor material.
- Enter the maximum acceptable voltage-drop percentage and select a current safety factor.
- Click Calculate Wire Size to view the suggested AWG, metric area, voltage drop, current and power loss.
How the Calculation Works
Calculating current from watts
When power is entered in watts, the tool estimates circuit current using voltage, phase and power factor. Three-phase calculations use the square root of three, while DC and single-phase calculations use their corresponding power relationships.
Calculating conductor area
The voltage-drop calculation uses conductor resistivity, current, cable length and allowable voltage loss. DC and single-phase circuits use the complete outgoing and returning path. Three-phase circuits use a three-phase length factor.
Selecting a standard size
The calculator finds the first standard conductor that satisfies both the calculated cross-sectional area and the estimated required ampacity. This prevents the result from relying on voltage drop alone.
Common AWG Wire Sizes
| AWG size | Area | Typical use | Important note |
|---|---|---|---|
| 14 AWG | 2.08 mm² | Light branch circuits | Subject to local small-conductor rules |
| 12 AWG | 3.31 mm² | General receptacle circuits | Installation conditions affect capacity |
| 10 AWG | 5.26 mm² | Higher-load circuits | Often used when distance increases |
| 8 AWG | 8.37 mm² | Appliances and equipment | Terminal temperature rating matters |
| 6 AWG | 13.30 mm² | Large appliances and feeders | Check overcurrent protection requirements |
| 4 AWG | 21.15 mm² | Feeders and heavy loads | Use approved cable and connectors |
Factors That Affect Wire Size
Load current
Higher electrical current normally requires a conductor with a larger cross-sectional area to control heating and electrical resistance.
Cable length
Electrical resistance increases with conductor length. A long cable run may therefore require a larger conductor to maintain acceptable voltage at the connected equipment.
Copper or aluminum
Copper has lower electrical resistivity than aluminum. An aluminum conductor generally requires a larger cross-sectional area to achieve similar resistance and voltage-drop performance.
Installation conditions
Ambient temperature, insulation type, conductor bundling, raceway fill, installation method and terminal ratings can reduce allowable current. These conditions must be checked separately.
Continuous loads
Loads that operate for extended periods may require additional sizing considerations. The safety-factor option can provide a basic planning margin, but it does not replace applicable electrical-code calculations.
Frequently Asked Questions
The answer depends on local electrical rules, conductor material, insulation, terminals, cable length and installation method. A longer circuit may need a larger size than the minimum ampacity requirement because of voltage drop.
Enter the one-way distance from the source to the load. The calculator automatically applies the appropriate circuit-length factor for DC, single-phase or three-phase calculations.
Voltage drop is the reduction in voltage that occurs as current travels through a conductor with electrical resistance. Excessive drop may affect the performance of motors, lights and sensitive equipment.
Copper has lower resistivity and normally needs a smaller cross-sectional area. Aluminum is lighter and can be economical for larger installations, but it requires approved terminals, installation practices and usually a larger conductor size.
Use the result only as an initial estimate. Final conductor selection should be verified against the electrical code used in your location and approved by a qualified electrician or electrical engineer.
A longer conductor has more total resistance. Increasing the conductor area lowers resistance and helps reduce voltage loss and power dissipation across the cable run.