Watts to Amps Calculator
This Watts to Amps calculator (also known as an Amps to Watts calculator or amperage calculator) helps you understand the relationship between electrical power and current. Use it to convert watts to amps or amps to watts for DC circuits, single-phase AC, and three-phase AC systems.
The Convention of Using Watts, Amps, and Volts
When talking about fundamental electrical quantities, we consider a few key physical quantities: resistance (R), voltage (V), and current (I). Electric current is also related to power (P). The SI unit of voltage is a volt (V), the unit of current is an ampere (A), and the unit of power is a watt (W).
These units — volts, amps, and watts — describe voltage, current, and power respectively. This convention is widely used in electrical engineering. Whenever someone wants to convert amps to watts or watts to amps, they are looking for the relationship between electrical current and power.
How to Convert Watts to Amps or Amps to Watts?
To convert watts to amps, you also need to know the voltage and the type of current. There are three main types of electrical current:
- DC (Direct Current)
- AC — Single-Phase current
- AC — Three-Phase current, which can be further divided into:
- Delta connection — referring to Line-to-Line Voltage (VLL)
- Star connection — referring to Line-to-Neutral Voltage (VLN)
How to Calculate Watts (Formulas)
DC Current
For direct current, the formula is the simplest:
I = P / V
where:
- I = current in amperes (A)
- P = power in watts (W)
- V = voltage in volts (V)
AC Single-Phase Current
For single-phase alternating current, the power factor (PF) must be included:
I = P / (V × PF)
where PF (Power Factor) ranges from 0 to 1. Typical value for AC motors: 0.80–0.95.
AC Three-Phase Current — Line-to-Line (Delta)
For three-phase AC with line-to-line voltage measurement:
I = P / (√3 × VLL × PF)
AC Three-Phase Current — Line-to-Neutral (Star)
For three-phase AC with line-to-neutral voltage measurement:
I = P / (3 × VLN × PF)
The Difference Between Line-to-Line and Line-to-Neutral Voltages
In a three-phase AC system, there are two ways to measure voltage:
- Line-to-Line voltage (VLL) — the voltage measured between any two of the three phase conductors. Also called "phase-to-phase" voltage. In US systems: typically 208V, 480V, or 600V.
- Line-to-Neutral voltage (VLN) — the voltage measured between one phase conductor and the neutral wire. In US systems: typically 120V, 277V, or 347V.
The relationship between them is: VLL = √3 × VLN ≈ 1.732 × VLN
Common Voltage Values
American System (US)
| Application | Voltage | System |
|---|---|---|
| Residential outlets | 120V | Single-phase AC |
| Residential large appliances | 240V | Single-phase AC |
| Light commercial | 208V | Three-phase AC (VLL) |
| Industrial motors | 480V | Three-phase AC (VLL) |
| Large industrial | 600V | Three-phase AC (VLL) |
Metric System (EU/International)
| Application | Voltage | System |
|---|---|---|
| Low-voltage DC (vehicles, solar) | 12V / 24V | DC |
| Residential and commercial | 220–230V | Single-phase AC |
| Industrial three-phase | 380–400V | Three-phase AC (VLL) |
Power Units Supported
This calculator supports both metric and American/Imperial power units:
| Unit | Symbol | Equivalent in Watts | System |
|---|---|---|---|
| Watt | W | 1 W | Metric (SI) |
| Kilowatt | kW | 1,000 W | Metric (SI) |
| Megawatt | MW | 1,000,000 W | Metric (SI) |
| Milliwatt | mW | 0.001 W | Metric (SI) |
| Horsepower | HP | 746 W | American |
| BTU per hour | BTU/hr | ≈ 0.293 W | American |
How to Use the Watts to Amps Calculator
- Select the calculation direction: Watts → Amps or Amps → Watts.
- Enter the power value (for W→A mode) or the current value (for A→W mode).
- Select the unit for power or current from the dropdown.
- Choose the current type: DC, Single-Phase AC, Three-Phase (Line-to-Line), or Three-Phase (Line-to-Neutral).
- Enter the voltage. Use the preset buttons for common US values (120V, 240V, 480V, 600V) or European/metric values (12V, 24V, 220V, 380V).
- For AC circuits, enter the Power Factor (PF). The default is 0.85, which is typical for AC motors.
- Click Calculate to get instant results.
Practical Examples
Example 1: Household appliance (US, 120V, single-phase)
A 1,200W microwave oven runs on 120V single-phase AC with PF = 1.0:
I = 1200 / (120 × 1.0) = 10 A
Example 2: Industrial motor (US, 480V three-phase)
A 5 HP (3,730W) motor on 480V three-phase AC with PF = 0.85:
I = 3730 / (√3 × 480 × 0.85) = 3730 / 706.6 ≈ 5.28 A
Example 3: EU residential (220V single-phase)
A 2,000W electric heater on 220V single-phase AC with PF = 1.0:
I = 2000 / (220 × 1.0) ≈ 9.09 A
Example 4: DC circuit (car battery, 12V)
A 100W car headlight on 12V DC:
I = 100 / 12 ≈ 8.33 A