Electrical Load Calculator
Estimate current draw (amps) from watts, voltage, and power factor for 1-phase or 3-phase systems.
Your Load Estimate
- Enter watts - Use the total real power (W) for the load or equipment.
- Set voltage - Use the nominal system voltage.
- Pick phase - Three-phase uses √3 relationships.
- Enter power factor - If unknown, 1.00 is a conservative simplification for planning.
- Breaker planning - Continuous loads often use a 125% planning factor before selecting a standard breaker size.
A 3,000 watt load on a 120 volt single-phase circuit draws 25 amps. Treated as a continuous load - the default here - that calls for a 35 amp breaker (25 A × 1.25 = 31.25, rounded up to the next standard size); turn continuous off and it is a 25 amp breaker. At power factor 1 the real power is 3 kW and the apparent power is 3 kVA, and the two only diverge once motors pull the power factor below 1. This tool handles the watts-to-amps and breaker step; for a full dwelling service, total your VA by the NEC method first, then enter the sum here.
Adding Loads Into One Current
How Do I Calculate Electrical Load?
An electrical load estimate converts power (watts) into current (amps) based on system voltage, phase, and (optionally) power factor. It's useful for planning circuits, comparing equipment, and getting a rough sense of service or feeder demand.
For many resistive loads (heaters, incandescent lighting), watts are close to real power. For motors and some electronics, power factor can matter, which is why this calculator shows both kW and kVA when applicable.
Example: a 3,000W load at 240V single-phase draws about 12.5A (before any start-up or duty-cycle considerations). For breaker planning, use this result as a baseline and then verify with equipment specs and local requirements.
Electrical Load vs Watts/Amps/Volts: Which Tool Should You Use?
These tools both output amps, but they're meant for different scales of work.
Use Electrical Load Calculator to total multiple devices/circuits (a mini “load schedule”), especially when you need a combined amp draw.
Use Watts/Amps/Volts for quick conversion of a single device or a single circuit.
After you estimate total amps, you can move on to Breaker Size, Wire Size, and Voltage Drop for planning.
Example Load List (Sum of Multiple Items)
| Item | Watts | Amps @ 120V (approx.) |
|---|---|---|
| LED lighting (whole area) | 300 W | 2.5 A |
| Refrigerator | 600 W | 5.0 A |
| Microwave | 1200 W | 10.0 A |
| Small appliance load | 900 W | 7.5 A |
| TOTAL | 3000 W | 25.0 A |
Example only. Real loads vary and many appliances have different starting/continuous behavior.
Load Calculation Formulas
This calculator totals multiple items into a single estimated current. It supports both simple single‑phase estimates and three‑phase approximations.
Three‑phase (PF≈1) = Amps ≈ Watts ÷ (√3 × Volts)
Total load = Total watts = sum of all item watts before converting to amps
If you're only converting one device, the Watts/Amps/Volts calculator is simpler. If you're adding many loads, a clear item list is the key.
Code Note
- The formal way to size a dwelling service is the NEC optional method: 3 VA per square foot for general lighting, 1,500 VA for each small-appliance and laundry circuit, plus appliances at nameplate, with the first 10 kVA at 100 percent and the remainder at 40 percent. This calculator performs the final watts-to-amps and breaker step - total those VA figures first, then enter the sum here.NFPA 70 (NEC) 220.82 - Optional Dwelling Load Calculation
Next Steps
With the load current in hand, size the circuit:
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Calculate total load before sizing your breaker and wire. Browse the electrical calculator collection.