Electrical
Watt Calculator
Separate real power from apparent power when comparing a single-phase or balanced three-phase electrical load.
Result
Electrical work is life-safety work governed by the NEC or your local code, and must be designed and installed by a licensed electrician. Conductor and overcurrent sizing depends on ambient temperature, conductor bundling, termination ratings, continuous-load rules and more. This is an educational estimate and must never be used as the basis for an installation.
Get a Free Business AuditWhat moves the number
- Voltage and current must come from the same load condition.
- The phase selection changes the relationship between line current and total power.
- Power factor controls the share of apparent power represented by real watts.
Where this one goes wrong
Entering motor shaft output as though it were electrical input skips conversion losses. This tool calculates power from electrical quantities; it does not estimate motor efficiency or certify that a supply can start the connected equipment.
Questions
About this calculator
Why do watts and volt-amps differ?
The power-factor input relates real power to apparent power. A low value changes watts without removing the current the supply and wiring must carry.
Which voltage belongs in the three-phase mode?
Use line-to-line voltage with line current for the balanced-load equation. An unbalanced installation needs a more detailed assessment.
Can I choose equipment capacity from these watts?
Treat the result as a planning check. Code requirements, equipment ratings and starting behavior still govern capacity selection; the heat equivalent is not a room-load calculation.
The formula
single phase: W = V × A × PF; three phase: W = V × A × √3 × PF
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How to use this calculator
- Voltage (V). Enter your own figure; the page starts at 240.
- Current (A). Enter your own figure; the page starts at 20.
- Phase. Enter your own figure; the page starts at Single phase.
- Power factor. Enter your own figure; the page starts at 1.
The result updates as you type, so you can try a figure, see what it does to real power, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Voltage (V) | 240 |
| Current (A) | 20 |
| Phase | Single phase |
| Power factor | 1 |
What comes out
| Result | Value |
|---|---|
| Real power main result | 4,800 |
| Kilowatts | 4.8 |
| Apparent power | 4,800 |
| Heat equivalent | 16,378 |
240 V at 20 A single-phase is 4,800 watts (4.8 kW), or 4,800 VA apparent power.
How sensitive the answer is
Holding everything else steady and changing only voltage (v), this is what happens to real power. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Voltage (V) | Real power |
|---|---|
| 120 | 2,400 |
| 180 | 3,600 |
| 240 example above | 4,800 |
| 360 | 7,200 |
| 480 | 9,600 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Voltage (V)
- A number, between 0 and 1000000, starting at 240.
- Current (A)
- A number, between 0 and 100000, starting at 20.
- Phase
- Choose from Single phase, Three phase.
- Power factor
- A number, between 0 and 1, starting at 1.
What the results tell you
| Result | What it is |
|---|---|
| Real power | The headline result. A number. |
| Kilowatts | A decimal figure. |
| Apparent power | A number. |
| Heat equivalent | A number. |
Before you rely on this number
Conductor sizing, voltage drop and load figures are governed by code, and the code takes precedence over any calculator. Ambient temperature, conduit fill, continuous load factors and the specific installation all change the answer. Treat this as a first pass, not a design.
Keep going
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