Wire Gauge (AWG) Calculator

Enter your load current, run length, voltage, and conductor material to get the recommended AWG gauge, voltage drop, and a full comparison table of all standard gauges.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter Load Current (A)
Input the continuous current draw of your electrical load in amperes. This is crucial for sizing.
2
Specify One-Way Run Length (ft)
Enter the distance from your electrical panel to the device or outlet in feet. Total circuit length is double this for voltage drop.
3
Input Supply Voltage (V)
Provide the system voltage, typically 120V for standard outlets or 240V for larger appliances.
4
Select Conductor Material
Choose between Copper or Aluminum, as their conductive properties differ significantly.
5
Review your results
The calculator will recommend the appropriate AWG wire gauge, considering NEC ampacity and voltage drop limits.

Example Calculation

A homeowner needs to run power to a new 20A circuit for a workshop. The one-way distance is 50 feet, and the supply voltage is 120V, using copper wire.

Load Current (A)

One-Way Run Length (ft)

Supply Voltage (V)

120

Conductor Material

copper

Results

10 AWG

Tips

Prioritize Safety Margins

Always select a wire gauge that comfortably exceeds the minimum requirements for ampacity and voltage drop. A 15-20% safety margin ensures reliable performance and longevity.

Consider Conduit Fill

When running multiple wires in a conduit, factor in the conduit fill limits to prevent overheating. Over-filling can lead to derating of wire ampacity, requiring larger gauges.

Consult Local Codes

While the NEC provides national standards, always consult your local electrical codes. Some jurisdictions have stricter requirements or specific amendments that must be followed for compliance.

The Wire Gauge (AWG) Calculator is an essential tool for electricians, DIY enthusiasts, and engineers to correctly size electrical wiring for various applications. It ensures compliance with safety standards by factoring in load current, run length, supply voltage, and conductor material. For a 20A workshop circuit with a 50-foot run at 120V using copper wire, the calculator recommends 10 AWG wire to maintain voltage drop under the critical 3% threshold, thereby preventing inefficient operation and potential safety hazards.

National Electrical Code (NEC) Compliance for Wiring

In electrical engineering, adherence to the National Electrical Code (NEC) is paramount for safety and functional integrity. The NEC, published by the National Fire Protection Association (NFPA), sets the standards for safe electrical installation. Article 310 of the NEC, for instance, provides extensive tables for conductor ampacity based on wire gauge, material, and insulation temperature ratings. Crucially, it also mandates limits for voltage drop, generally recommending that the total voltage drop for feeder and branch circuits combined should not exceed 5%, with 3% often cited as a best practice for individual circuits to ensure efficient operation and prevent equipment damage. Compliance with these detailed regulations is not just a legal requirement but a fundamental engineering principle.

Determining Optimal Wire Gauge

Selecting the correct wire gauge involves balancing two primary factors: ampacity (the maximum current a wire can safely carry) and voltage drop (the acceptable loss of voltage over the wire's length). The calculation typically involves:

Ampacity Check: Ensure the chosen gauge meets or exceeds the load current based on NEC tables for the specific conductor material and insulation temperature.
Voltage Drop Check: Calculate the voltage drop using Ohm's Law and wire resistance.
```
Voltage Drop (V) = (2 × Run Length (ft) × Load Current (A) × Resistivity (Ω·cm/kft)) / 1000
```
Then, calculate the percentage:
```
Voltage Drop (%) = (Voltage Drop (V) / Supply Voltage (V)) × 100
```
For copper, resistivity is approximately 10.4 Ω·cm/kft; for aluminum, it's about 17.0 Ω·cm/kft. The "2" in the formula accounts for the round trip (supply and return).

💡 For estimating power consumption of specific devices, our Lighting Energy Cost Calculator can help assess the load on your circuits.

Sizing Wire for a Workshop Circuit: A Worked Example

A homeowner is installing a new 20A circuit for a workshop. The one-way run length from the panel to the outlet is 50 feet. The supply voltage is 120V, and they will be using copper wire.

Identify parameters:
- Load Current = 20 A
- One-Way Run Length = 50 ft (Total circuit length = 100 ft)
- Supply Voltage = 120 V
- Conductor Material = Copper (Resistivity ≈ 10.4 Ω·cm/kft)
Check ampacity:
- 14 AWG copper is rated for 15A (too small for 20A)
- 12 AWG copper is rated for 20A (meets ampacity)
- 10 AWG copper is rated for 30A (exceeds ampacity)
Calculate voltage drop for 12 AWG copper:
- Resistivity for 12 AWG copper is approximately 1.98 Ω/1000 ft.
- Voltage Drop = (2 × 50 ft × 20 A × 1.98 Ω/1000 ft) / 1000 = 3.96 V
- Voltage Drop % = (3.96 V / 120 V) × 100 = 3.3%
Calculate voltage drop for 10 AWG copper:
- Resistivity for 10 AWG copper is approximately 1.24 Ω/1000 ft.
- Voltage Drop = (2 × 50 ft × 20 A × 1.24 Ω/1000 ft) / 1000 = 2.48 V
- Voltage Drop % = (2.48 V / 120 V) × 100 = 2.06%

Since 12 AWG results in a 3.3% voltage drop (exceeding the 3% recommendation), 10 AWG copper wire is the recommended gauge to ensure optimal performance and safety.

💡 To optimize power delivery for other electrical systems, our LED Panel Output Calculator can help you design efficient lighting setups.

The Origin of the American Wire Gauge Standard

The American Wire Gauge (AWG) standard has its roots in the 19th century, formally adopted in 1857 by the American electrical industry. It was developed from the older Birmingham Wire Gauge (BWG) system. The need for a standardized system arose with the rapid expansion of telegraphy and, later, electric power distribution, as inconsistent wire sizes led to confusion and safety issues. The AWG system is a logarithmic scale, meaning that the ratio of any two consecutive wire diameters is constant, and every three AWG steps approximately doubles or halves the wire's cross-sectional area. This mathematical progression provides a consistent and predictable relationship between gauge number, diameter, resistance, and current carrying capacity, which became crucial for the precise engineering of electrical systems.

Frequently Asked Questions

What is AWG wire gauge?

AWG, or American Wire Gauge, is a standardized system for denoting the diameter of electrical conductors. Lower AWG numbers correspond to thicker wires, which have lower resistance and can carry more current without overheating. Higher AWG numbers indicate thinner wires. This system is crucial for selecting the correct wire size for electrical circuits to ensure safety, prevent voltage drop, and comply with electrical codes like the National Electrical Code (NEC).

Why is voltage drop important?

Voltage drop is the reduction in electrical potential along a conductor due to its resistance, which increases with wire length and current. Excessive voltage drop, typically more than 3% in a circuit, can lead to inefficient operation of appliances, dimming lights, and overheating of motors. It's crucial for electrical system design to ensure that the voltage delivered to the load remains within acceptable limits for optimal performance and equipment longevity.

What is ampacity?

Ampacity refers to the maximum current, in amperes, that a conductor can continuously carry under specified conditions without exceeding its temperature rating. It is determined by factors such as wire gauge, conductor material (copper or aluminum), insulation type, ambient temperature, and installation method. Exceeding a wire's ampacity can cause overheating, leading to insulation degradation, fire hazards, and equipment damage. The National Electrical Code (NEC) provides tables for safe ampacity ratings.