Watts to Amps Calculator
Convert electrical power (watts) to current (amperage) for single-phase and three-phase systems.
Important Power-to-Current Conversion Notes
- • Always use nameplate values when available - calculated values may not account for all factors
- • Power factor significantly affects current - motors and fluorescent lights are not unity power factor
- • Three-phase calculations use line-to-line voltage, result is current per conductor
Watts to Amps Calculator
Convert watts to amps
Input Parameters
Calculation Results
Electrical Power Formulas Reference
Complete formula reference for converting watts to amps across different electrical systems.
| System Type | Formula | Example Calculation | Common Applications | Important Notes |
|---|---|---|---|---|
| Single-Phase AC | I = P ÷ (V × PF) | 1200 W ÷ (120 V × 1.0) = 10 A | Residential loads, small appliances | Most common residential calculation |
| Single-Phase DC | I = P ÷ V | 1200 W ÷ 12 V = 100 A | Battery systems, automotive, solar | No power factor consideration |
| Three-Phase Balanced | I = P ÷ (√3 × V × PF) | 10 kW ÷ (1.73 × 480 V × 0.85) = 14.2 A | Industrial motors, commercial loads | V is line-to-line voltage |
| Three-Phase Line Current | I_line = P ÷ (3 × V_phase × PF) | 10 kW ÷ (3 × 277 V × 0.85) = 14.2 A | Wye-connected loads | V_phase = V_line ÷ √3 |
| Apparent Power (VA) | I = S ÷ V (single-phase) | 1500 VA ÷ 120 V = 12.5 A | Transformers, reactive loads | Includes reactive power component |
Formula Key:
- • I = Current in Amperes • P = Power in Watts • V = Voltage • PF = Power Factor
- • √3 = 1.732 (square root of 3 for three-phase calculations)
- • For three-phase, use line-to-line voltage (480 V, 208 V, etc.)
Frequently Asked Questions
How do I convert 1500 watts to amps?▼
For single-phase: Amps = Watts ÷ Voltage. At 120 V: 1500 W ÷ 120 V = 12.5 A. At 240 V: 1500 W ÷ 240 V = 6.25 A. For three-phase: Amps = Watts ÷ (√3 × Voltage × Power Factor). Always check if power factor applies to your load type.
What is power factor and when do I use it?▼
Power factor (PF) is the ratio of real power to apparent power, ranging from 0 to 1. Use PF for inductive loads like motors, fluorescent lights, and transformers. Resistive loads like heaters have PF = 1.0.
Why do I get different amps at 120 V vs 240 V?▼
Same power at higher voltage requires lower current. This is why large appliances use 240 V - it reduces current by half, allowing smaller wire sizes and reducing voltage drop. Example: 2400 W load draws 20 A at 120 V but only 10 A at 240 V.
How do I calculate three-phase current?▼
Three-phase formula: I = P ÷ (√3 × V × PF). √3 = 1.732. Use line-to-line voltage (480 V, 208 V). Result is current per line.
What if my appliance shows both watts and amps?▼
Use the amp rating from the nameplate - it accounts for power factor and includes all electrical characteristics. Watts ÷ voltage might not match nameplate amps due to power factor, starting currents, or reactive components.
How does efficiency affect current calculations?▼
Input current is higher than calculated from output power due to losses. For motors, use efficiency ratings: Input Watts = Output Watts ÷ Efficiency.