Electrical reference chart
Watts to Amps Chart
Convert equipment watts, lighting watts, heater watts, or appliance watts into estimated circuit current for the voltage and phase serving the load.
Quick reference table
Watts-to-amps is the load-planning direction: start with a watt rating and estimate current. 1,500 W at 120 V draws about 12.5 A, while the same wattage at 240 V draws about 6.3 A. For AC equipment with power factor below 1.0, current rises above the simple unity-PF result.
Unity power-factor current from common watt loads
| Load watts | 120 V 1-phase | 208 V 1-phase | 240 V 1-phase | 480 V 3-phase |
|---|---|---|---|---|
| 750 W | 6.3 A | 3.6 A | 3.1 A | 0.9 A |
| 1,500 W | 12.5 A | 7.2 A | 6.3 A | 1.8 A |
| 3,000 W | 25.0 A | 14.4 A | 12.5 A | 3.6 A |
| 4,500 W | 37.5 A | 21.6 A | 18.8 A | 5.4 A |
| 9,000 W | 75.0 A | 43.3 A | 37.5 A | 10.8 A |
Before using the amp result for a circuit decision
| Watt source | Confirm first | Next calculator context |
|---|---|---|
| Portable appliance label | Voltage and duty cycle | Receptacle or branch-load review |
| Lighting layout total | Driver input watts and control zones | Lighting circuit or energy calculator |
| Space-heating load | Continuous operating assumption | Branch-circuit and load schedule review |
| Motor or compressor watts | PF, efficiency, and nameplate FLA | Motor-current calculator |
Watts-to-amps chart to calculator handoff
| Search or worksheet need | Use this chart for | Open the calculator when |
|---|---|---|
| Watts to amps chart | Screening current from a listed watt value at a common voltage | Voltage, phase, PF, and load basis must be saved with the result |
| 1500 watts to amps | Checking a common resistive or appliance-load estimate | The label voltage, duty cycle, or receptacle context changes the next step |
| Three-phase watts to amps | Separating line-to-line voltage from single-phase voltage rows | A balanced three-phase load and PF need one calculated current |
| Watts, VA, or kVA label | Deciding whether the label is real power or apparent power | The equipment label is VA/kVA or the task is transformer, UPS, or generator current |
How to use this chart
Start with the watt label
Use the wattage from a nameplate, submittal, lighting schedule, heater schedule, or appliance label and keep the source visible.
Choose the served voltage
Select the voltage actually feeding the load. A 120 V plug load, 208 V equipment load, and 240 V heater cannot share the same amp row.
Decide whether PF applies
For resistance heat the unity-PF row may be close, while motors and electronic power supplies need PF or manufacturer input data.
Use the amp result as a handoff
Carry the current into the calculator when the next decision involves circuit loading, conductor sizing, energy use, or documentation.
Formula basis
Single phase: A = W / (V x PF). Balanced three phase: A = W / (1.732 x VLL x PF).
- A is current in amperes.
- W is real load power in watts.
- V is voltage for DC or single-phase calculations.
- VLL is line-to-line voltage for balanced three-phase calculations.
- PF is power factor when applicable.
Worked examples
1,500 W countertop load at 120 V
1,500 / 120 = 12.5 A. Use that as an operating-current estimate, then check the actual circuit and appliance instructions.
9 kW heater at 240 V
9,000 / 240 = 37.5 A for a unity-PF resistance load before any continuous-load or equipment-specific review.
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Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.