Electrical Load Calculator
Not Every Watt Runs at Once
Adding up the nameplate wattage of every appliance on a circuit overstates the real draw, because not everything runs simultaneously at full output. Electrical designers apply a demand factor to connected load to get a more realistic figure for sizing conductors and services. This calculator totals appliance loads, applies that factor, and converts the result to a current draw at your system voltage.
The Formula
Demand Load = Connected Load × Demand Factor
Current = Demand Load / Voltage
Demand factor is expressed as a percentage of the connected load that's realistically expected to be in use at the same time; leaving it at 100% assumes every listed appliance draws its full rated load simultaneously.
A Worked Example
| Appliance Load | Wattage |
|---|---|
| Appliance 1 | 1500 W |
| Appliance 2 | 800 W |
| Appliance 3 | 1200 W |
| Connected Load | 3500 W |
At a 100% demand factor and 120 V: Current = 3500 ÷ 120 = 29.17 A.
Where This Calculation Matters
- Panel and service sizing — verifying a service's rated capacity can handle the intended mix of appliances and circuits.
- Kitchen and shop circuits — multiple high-wattage appliances (microwave, toaster, air fryer) often share a circuit, making total demand worth checking before overloading it.
- Adding a major appliance — checking whether an existing circuit or panel has headroom before installing an EV charger, hot tub, or workshop tool.
- Load studies — applying a realistic demand factor rather than raw nameplate totals for a more accurate capacity assessment.
How to Use This Calculator
- Enter each appliance's load in watts as a comma-separated list, for example
1500, 800, 1200. - Enter the circuit voltage.
- Optionally enter a Demand Factor as a percentage (defaults to 100% if left blank).
- Select Calculate to see the resulting current draw and demand load.
Related Calculations
Once you know the current, check it against a safe conductor size with the Wire Size Calculator, or verify long-run performance with the Voltage Drop Calculator.