⚡ Watts to Amps Calculator
Convert power (watts) to current (amperes)
How to Use This Calculator
Select Current Type
Choose DC (Direct Current) or AC (Alternating Current). For DC circuits, power factor is not needed. For AC circuits, power factor accounts for reactive loads.
Enter Power and Voltage
Input the power in watts (W) and voltage in volts (V). For AC, also enter the power factor (typically 0.7-1.0, use 1.0 for resistive loads).
Calculate
Click "Calculate Current" to get the current in amperes (A). This helps determine circuit breaker sizing, wire gauge selection, and safety requirements.
Formula
I = P / V
DC Current
I = P / (V × PF)
AC Current
Where:
- I = Current (Amperes, A)
- P = Power (Watts, W)
- V = Voltage (Volts, V)
- PF = Power Factor (dimensionless, 0 ≤ PF ≤ 1)
Example Calculation 1 (DC):
For P = 1,200 W, V = 120 V:
I = P / V = 1,200 / 120 = 10 A
A 1,200W DC device at 120V draws 10 amperes of current.
Example Calculation 2 (AC - Resistive Load):
For P = 1,200 W, V = 120 V, PF = 1.0:
I = P / (V × PF) = 1,200 / (120 × 1.0) = 10 A
A 1,200W resistive AC load (like a heater) at 120V with PF = 1.0 draws 10 amperes.
Example Calculation 3 (AC - Inductive Load):
For P = 1,200 W, V = 120 V, PF = 0.8:
I = P / (V × PF) = 1,200 / (120 × 0.8) = 1,200 / 96 = 12.5 A
A 1,200W motor at 120V with PF = 0.8 draws 12.5 amperes (higher due to lower power factor).
About Watts to Amps Calculator
The Watts to Amps Calculator converts electrical power (watts) to current (amperes). For DC circuits, current equals power divided by voltage (I = P / V). For AC circuits, current also depends on power factor: I = P / (V × PF). Power factor accounts for reactive loads like motors and transformers. This calculator is essential for circuit design, wire sizing, and safety calculations.
When to Use This Calculator
- Circuit Breaker Sizing: Determine appropriate circuit breaker rating
- Wire Gauge Selection: Calculate current to select proper wire size
- Safety Analysis: Verify circuits can handle calculated current
- Power Supply Design: Size power supplies based on load current
- Electrical Installation: Ensure compliance with electrical codes
Why Use Our Calculator?
- ✅ DC and AC Support: Handles both direct and alternating current
- ✅ Power Factor: Accounts for reactive loads in AC circuits
- ✅ Quick Calculation: Instantly convert power to current
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn power, voltage, and current relationships
Common Applications
Circuit Breaker Sizing: Electrical codes require circuit breakers sized for load current. For a 1,500W heater at 120V: I = 1,500 / 120 = 12.5 A. Use a 15A or 20A circuit breaker (with 125% margin). This prevents overload and ensures safety. The calculator helps select appropriate breaker ratings.
Wire Gauge Selection: Wire size (AWG) depends on current. For 10A at 120V: I = 10 A. A 14 AWG wire can handle ~15A, so it's suitable. For higher currents, larger wire (lower AWG number) is needed. NEC (National Electrical Code) specifies ampacity limits for each wire gauge. This calculator helps ensure proper wire sizing.
Motor Current Calculation: Motors have lower power factors (0.7-0.9), increasing current for the same power. A 1,200W motor at 120V with PF = 0.8 draws: I = 1,200 / (120 × 0.8) = 12.5 A (vs. 10A for resistive load). This affects breaker and wire sizing. Always use actual motor power factor when calculating.
Tips for Best Results
- For DC circuits, power factor is always 1.0
- For resistive AC loads (heaters, incandescent lights), use PF = 1.0
- For motors and inductive loads, typical PF = 0.7-0.9
- Add 25% margin for circuit breaker sizing (1.25 × calculated current)
- Use RMS values for AC voltage and current
Frequently Asked Questions
Why is power factor needed for AC?
Power factor accounts for reactive power in AC circuits. For resistive loads (heaters, lights), PF = 1.0, so I = P / V. For reactive loads (motors, transformers), PF < 1.0, increasing current for the same real power. Lower PF means more current, requiring larger wires and breakers. Always use actual power factor for accurate calculations.
What power factor should I use?
For resistive loads (heaters, incandescent lights): PF = 1.0. For motors: PF = 0.7-0.9 (check motor nameplate). For typical household loads: PF = 0.85-0.95. For pure resistive circuits: PF = 1.0. If unsure, use PF = 0.85 as a conservative estimate, or check device specifications.
How do I size a circuit breaker from calculated current?
Multiply calculated current by 1.25 (125% rule) for continuous loads, then round up to nearest standard breaker size. For example: 12.5 A × 1.25 = 15.6 A → use 20A breaker. Standard sizes: 15A, 20A, 30A, 40A, 50A, etc. Never exceed wire ampacity rating. Always follow local electrical codes.
Is this the same as apparent current?
This calculator gives real current for real power consumption. For AC with reactive loads, apparent current (I_apparent = P / V) is lower than real current (I_real = P / (V × PF)). Real current is used for wire sizing and breaker selection. Apparent power is S = V × I_apparent, while real power is P = V × I_real × PF.
Can I use this for three-phase calculations?
This calculator is for single-phase. For three-phase: I = P / (√3 × V × PF), where V is line-to-line voltage. For example, 10 kW at 480V three-phase with PF = 0.9: I = 10,000 / (√3 × 480 × 0.9) = 13.4 A per phase. Use a three-phase calculator for accurate three-phase current calculations.