Watts to Amps Calculator
To convert watts to amps, use real electrical input power and the supply voltage. DC uses I = P/V; AC calculations also require power factor and, for three-phase systems, the correct voltage type.
Calculate current from watts
Choose the system type, then enter real input power and supply voltage.
Calculated current
A
mA
I = P / V
—
Idealized DC load current at the voltage entered. Battery voltage can vary.
Interactive calculator loading. Static formulas remain available below.
Theoretical current only. Cable, breaker and protective-device selection require a separate electrical design.
Initial example: 120 W at 24 V DC = 5 A. Mode changes keep your inputs; they do not convert line-to-line voltage into line-to-neutral voltage.
Watts to Amps Formula
Current depends on the electrical system, not on watts alone. Use the formula that matches the supply.
| Sistem | Formula | Input definition |
|---|---|---|
| DC | I = P / V | DC load input power and terminal voltage |
| Single-phase AC | I = P / (V × PF) | Real input power, RMS voltage and true power factor |
| Balanced three-phase AC, line-to-line | I = P / (√3 × VLL × PF) | Total three-phase real power and RMS line-to-line voltage |
| Balanced three-phase wye, line-to-neutral | I = P / (3 × VLN × PF) | Total three-phase real power and RMS line-to-neutral voltage |
I is current in amperes (A), P is real power in watts (W), V is voltage in volts, and PF is true power factor. One ampere equals 1,000 milliamperes (mA). Three-phase results are line current, not delta winding current or neutral current.
Illustrative example: a 120 W DC load operating at 24 V draws 120 ÷ 24 = 5 A, or 5,000 mA. This is a calculation example, not a measured INLUX product specification.
How to Calculate Amps from Watts
- Identify the supply: DC, single-phase AC or balanced three-phase AC.
- Enter the load’s real electrical input power. For three-phase mode, enter the total power across all three phases.
- Enter the operating voltage. For AC, use RMS voltage and select the correct three-phase voltage type.
- Enter measured or nameplate true power factor for AC. The example value of 0.90 is not a universal LED specification.
- Read the current, substituted formula and assumptions together. Confirm the result against equipment data before using it in a design.
The calculator accepts plain decimal numbers with a period. Mode changes retain your values, so check their meaning after switching. Voltage presets change the voltage field only; they do not identify the supply or convert line voltage to phase voltage.
DC Watts to Amps
For a steady DC load at a stated voltage, divide input watts by volts. For example, 100 W at 12 V is about 8.3333 A. At 24 V, the same 100 W load is about 4.1667 A. A higher voltage means less current for the same input power, within the assumptions of this calculation.
Use operating terminal voltage rather than treating a battery’s nominal voltage as constant under every condition.
Single-Phase AC Calculations
Single-phase AC uses I = P/(V × PF). Real power is measured in watts; apparent power is measured in volt-amperes (VA). True power factor is real power divided by apparent power. It is not the same as energy-conversion efficiency, and it can include the effect of a nonsinusoidal current waveform.
Illustrative example: 150 W at 230 V RMS with PF = 0.95 gives 150 ÷ (230 × 0.95) ≈ 0.6865 A. If PF is unknown, the calculator cannot establish the current from real watts and voltage alone.
Three-Phase AC Calculations
For a balanced three-phase load, use total real power and the voltage convention that matches the measurement. With line-to-line RMS voltage, use the √3 formula. With line-to-neutral RMS voltage in a balanced wye system, use the factor of 3.
Illustrative line-to-line example: 12,000 W at 400 V RMS and PF = 0.90 gives 12,000 ÷ (√3 × 400 × 0.90) ≈ 19.245 A.
Illustrative line-to-neutral example: 12,000 W at 230 V RMS and PF = 0.90 gives 12,000 ÷ (3 × 230 × 0.90) ≈ 19.3237 A. These examples differ because 230 × √3 is not exactly 400. The calculator does not automatically convert between voltage types.
These three-phase formulas assume balanced operation and the usual sinusoidal supply-voltage relationship. Unbalanced loads or atypical supply waveforms require further analysis; do not use this result to determine each phase’s worst-case current or neutral current.
Watts to Amps Conversion Charts
All chart values below are current in amperes, calculated from real input watts and rounded to four decimal places. AC charts state their power-factor assumption. They are examples for comparison, not equipment ratings or design limits.
| Real input power | 12 V | 24 V | 48 V |
|---|---|---|---|
| 50 W | 4.1667 | 2.0833 | 1.0417 |
| 100 W | 8.3333 | 4.1667 | 2.0833 |
| 120 W | 10 | 5 | 2.5 |
| 200 W | 16.6667 | 8.3333 | 4.1667 |
| 500 W | 41.6667 | 20.8333 | 10.4167 |
| 1000 W | 83.3333 | 41.6667 | 20.8333 |
Calculated using I = P / (V × PF), with PF = 1.0. Power is real electrical input power in watts (W); voltage is measured across the single-phase load in RMS volts (V). Values are RMS current in amperes (A), rounded to four decimal places. These are illustrative calculations, not equipment ratings.
| Real input power | 120 V | 230 V | 240 V |
|---|---|---|---|
| 50 W | 0.4167 | 0.2174 | 0.2083 |
| 100 W | 0.8333 | 0.4348 | 0.4167 |
| 120 W | 1 | 0.5217 | 0.5 |
| 200 W | 1.6667 | 0.8696 | 0.8333 |
| 500 W | 4.1667 | 2.1739 | 2.0833 |
| 1000 W | 8.3333 | 4.3478 | 4.1667 |
Calculated using I = P / (V × PF), with PF = 0.90. Power is real electrical input power in watts (W); voltage is measured across the single-phase load in RMS volts (V). Values are RMS current in amperes (A), rounded to four decimal places. PF = 0.90 is an example, not a universal LED driver specification.
| Real input power | 120 V | 230 V | 240 V |
|---|---|---|---|
| 50 W | 0.463 | 0.2415 | 0.2315 |
| 100 W | 0.9259 | 0.4831 | 0.463 |
| 120 W | 1.1111 | 0.5797 | 0.5556 |
| 200 W | 1.8519 | 0.9662 | 0.9259 |
| 500 W | 4.6296 | 2.4155 | 2.3148 |
| 1000 W | 9.2593 | 4.8309 | 4.6296 |
LED Lighting Applications
Use the complete fixture’s electrical input power when estimating supply current. LED module output wattage does not automatically equal AC driver input wattage.
Driver efficiency describes how much input power reaches its output. Power factor describes the relationship between real input power and apparent input power. A driver can have different values for these two quantities; neither should be substituted for the other.
For project work, obtain input power, rated voltage and true PF for the exact driver or luminaire configuration. Starting current, operating temperature and protective-device requirements need separate consideration. No model-specific PF or driver-efficiency claim is used in the examples on this page.
Solar PV and Battery Applications
P/V estimates instantaneous DC load current at the stated terminal voltage. Actual battery charge or discharge current changes with voltage, load, controller operation and losses. Current alone does not establish battery capacity, usable energy or operating time.
PV panel rated power is measured under specified test conditions. Dividing a panel’s STC wattage by battery voltage does not establish actual charging current. PV operating voltage, irradiance and the charge controller’s conversion behavior matter. This calculator is a load-current conversion tool, not an MPPT charging or battery-runtime model.
Common Calculation Mistakes
- Using watts without specifying voltage.
- Entering VA as though it were real watts.
- Assuming PF = 1 for every AC load, or substituting driver efficiency for PF.
- Entering per-phase watts into a formula that expects total three-phase power.
- Confusing line-to-line and line-to-neutral RMS voltage.
- Using LED output watts instead of supply-side input watts.
- Interpreting theoretical current as a cable, breaker or protection-device selection.
Soalan Lazim
Can you convert watts to amps without volts?
No. Current depends on voltage. AC calculations using real watts also need true power factor and the system configuration.
How many amps is 100 watts?
For DC, 100 W at 12 V is about 8.3333 A; at 24 V it is about 4.1667 A. For single-phase 120 V AC at PF = 1, it is about 0.8333 A. Change the voltage or PF and the answer changes.
Is power factor the same as LED driver efficiency?
No. PF compares real input power with apparent input power. Efficiency compares useful output power with real input power.
Which three-phase voltage should I enter?
Select line-to-line if your voltage is measured between two supply lines. Select line-to-neutral only for the balanced wye calculation. Both modes require total three-phase real power.
Why does a small result use scientific notation?
Scientific notation keeps a positive current from appearing as zero after decimal rounding. For example, 1e-6 A means 0.000001 A. Unsupported extreme values produce an error instead of an unreliable result.
Does this amperage calculator select a breaker or cable?
No. Cable and protective-device selection also depends on installation conditions, applicable electrical requirements, fault protection, equipment data and other design factors. Use a separate qualified electrical design process.
Are the preset values verified operating conditions?
No. They are convenient voltage entries. Verify the actual supply voltage, phase configuration, power and PF for your equipment.
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