Electrical Breaker Calculator

This electrical breaker calculator helps you determine the correct breaker size for your electrical circuit based on wire gauge and ampacity. Proper breaker sizing is essential for safety and compliance with electrical codes.

How to Use This Calculator

To use this electrical breaker calculator:

Select the wire gauge from the dropdown menu
Enter the number of conductors in your circuit
Select the conductor material (copper or aluminum)
Click the "Calculate" button

The calculator will display the recommended breaker size based on the National Electrical Code (NEC) standards. You can also view a chart showing the relationship between wire gauge and breaker size.

Formula Used

The electrical breaker calculator uses the following formula to determine the recommended breaker size:

Recommended Breaker Size = (Conductor Ampacity × 125%) / Number of Conductors

Where:

Conductor Ampacity is determined by the wire gauge and material
125% is the derating factor for multiple conductors
Number of Conductors is the total number of wires in the circuit

The calculator uses standard ampacity values from the NEC for copper and aluminum conductors.

Worked Examples

Example 1: 12 AWG Copper Wire

For a 12 AWG copper wire with 3 conductors:

Conductor Ampacity = 20A (standard for 12 AWG copper)
Apply derating factor: 20A × 1.25 = 25A
Divide by number of conductors: 25A / 3 = 8.33A
Round up to standard breaker size: 15A

The recommended breaker size is 15A.

Example 2: 10 AWG Aluminum Wire

For a 10 AWG aluminum wire with 2 conductors:

Conductor Ampacity = 35A (standard for 10 AWG aluminum)
Apply derating factor: 35A × 1.25 = 43.75A
Divide by number of conductors: 43.75A / 2 = 21.875A
Round up to standard breaker size: 25A

The recommended breaker size is 25A.

Note: Always select a breaker size that matches or exceeds the calculated value for safety. Never use a breaker smaller than the calculated size.

Breaker Size Chart

Here's a reference table showing standard breaker sizes and their corresponding wire gauges:

Wire Gauge	Copper Ampacity (A)	Aluminum Ampacity (A)	Recommended Breaker Size
14 AWG	15	12	15A
12 AWG	20	25	20A
10 AWG	30	35	30A
8 AWG	50	55	50A
6 AWG	65	70	65A

Frequently Asked Questions

Why is my calculated breaker size different from the chart?: The chart shows standard values, but the calculator applies a 125% derating factor for multiple conductors. If you have only one conductor, the calculated size will match the chart value.
Can I use a breaker larger than the calculated size?: Yes, you can use a larger breaker, but it must be rated for the voltage of your circuit. Never use a smaller breaker than calculated for safety reasons.
What happens if I use the wrong breaker size?: Using a breaker that's too small can cause overheating and fire hazards. Using a breaker that's too large can cause nuisance tripping and may not provide adequate protection.
Does this calculator account for voltage drop?: No, this calculator focuses on breaker sizing. For voltage drop calculations, you would need to consider wire length and resistance factors.
Where can I find more information about electrical codes?: The National Electrical Code (NEC) is published by the National Fire Protection Association (NFPA). You can find official copies on their website or through local electrical inspectors.