Electrical Load Calculator
Calculate the total electrical power load (Watts) and current (Amps) of home appliances to estimate breaker and subpanel sizes.
Calculation Results
The combined total wattage of all input appliance loads.
The estimated electrical current load in Amperes at the selected service voltage.
How This Calculator Works
To calculate household electrical loads:
- Enter the wattage rating of your lighting/outlets, HVAC systems, and heavy appliances.
- Specify the system operating voltage (240V is standard for complete panel estimates; 120V is used for single branch lines).
- The calculator determines total active wattage and panel amperage loading.
Formula & Calculations
Electrical load calculations translate power (Watts) to active current (Amps) using Ohm's Law:
Total Power (Watts) = Sum of all individual appliance wattages
Amperage (Amps) = Total Power (Watts) / System Voltage (Volts)
For standard US residential houses, a double-pole 240V connection handles heavy heating loads, while outlets use single-pole 120V loops.
Step-by-Step Calculation Examples
Standard Small Home Load Profile
Calculating total panel wattage and required service amperage at 240V for typical household appliances.
- lighting_watts: 1200
- ac_watts: 3500
- dryer_watts: 5000
- range_watts: 8000
- other_watts: 1500
- voltage: 240
- total_watts: 19200
- total_amps: 80.0
Frequently Asked Questions
What size electrical service panel does a standard home need?
Modern building codes require a minimum of 100 Amp service for new homes. Homes with electric heat, central AC, or EV charging stations typically install 200 Amp or 400 Amp panels.
How do you convert Watts to Amps?
Divide the wattage by the operating voltage. For example: a 1,200 Watt microwave running on a 120 Volt circuit draws exactly 10 Amps (1,200 / 120 = 10).
What is the continuous load rule?
According to the National Electrical Code (NEC), branch circuits must not load beyond 80% of their maximum breaker rating for continuous loads (loads that run for 3 hours or more).
How many Watts can a 20 Amp breaker handle?
On a standard 120V line, a 20 Amp breaker can handle up to 2,400 Watts (20 × 120). Under the 80% continuous load rule, you should limit this to 1,920 Watts.
What appliances run on 240V in a home?
Heavy appliances like central air conditioners, electric clothes dryers, ranges/ovens, water heaters, and electric vehicle chargers run on 240 Volts.