Electrical calculator
Circuit Breaker Sizing Calculator
Calculate the appropriate circuit breaker size for a load.
About the circuit breaker sizing calculator
The circuit breaker sizing calculator finds the appropriate breaker size for a given electrical load, accounting for continuous load requirements.
How to use this calculator
- 1
Enter load wattage
Enter the total wattage of the load.
- 2
Enter voltage
Enter the system voltage.
- 3
Choose load type
Select whether the load runs continuously (3+ hours).
How the calculation works
NEC: Continuous loads require 125% sizing. Breaker = load current × 1.25 (if continuous), rounded up to standard size.
Example: 1800W at 120V continuous: 15A × 1.25 = 18.75A → 20A breaker.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about circuit breaker sizing calculator
How accurate is the circuit breaker sizing calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.