Electrical
Amp Calculator
Estimate running current from electrical input power, then inspect how the continuous-load selection changes the planning current.
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. Continuous loads must be sized at 125% under the NEC. The suggested breaker ignores conductor ampacity, which must also be checked.
Get a Free Business AuditWhat moves the number
- Use input watts rather than a motor's mechanical output rating.
- Actual supply voltage affects the calculated current for a fixed power.
- Phase, power factor and load duration have separate effects on the result.
Where this one goes wrong
The suggested breaker is a simplified numerical lookup. It does not check the wire, equipment-specific protection limits or available fault current. A plausible amperage must not become an installation instruction.
Questions
About this calculator
Why are two current values shown?
One is the estimated operating current. The sizing value applies the tool's duration assumption, so it can be higher without implying that the appliance consumes more power.
What if the equipment already lists input current?
Compare that rating and its stated conditions with the estimate. A conversion based on guessed power factor should not override manufacturer information.
Is the suggested breaker approved for this load?
No. This is a code-governed planning check, and final protection depends on the adopted rules, conductor conditions and the equipment listing.
The formula
A = W ÷ (V × PF) single phase; A = W ÷ (V × √3 × PF) three phase
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How to use this calculator
- Power (watts). Enter your own figure; the page starts at 4,800.
- Voltage (V). Enter your own figure; the page starts at 240.
- Phase. Enter your own figure; the page starts at Single phase.
- Power factor. Enter your own figure; the page starts at 1.
- Load type. Enter your own figure; the page starts at Continuous (3+ hours).
The result updates as you type, so you can try a figure, see what it does to current, 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 |
|---|---|
| Power (watts) | 4,800 |
| Voltage (V) | 240 |
| Phase | Single phase |
| Power factor | 1 |
| Load type | Continuous (3+ hours) |
What comes out
| Result | Value |
|---|---|
| Current main result | 20.0 |
| Current for sizing | 25.0 |
| Suggested breaker | 25 A |
| Power in kW | 4.8 |
4,800 W at 240 V draws 20.0 amps. Sizing at 25.0 A suggests a 25 A breaker.
How sensitive the answer is
Holding everything else steady and changing only power (watts), this is what happens to current. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Power (watts) | Current |
|---|---|
| 2,400 | 10.0 |
| 3,600 | 15.0 |
| 4,800 example above | 20.0 |
| 7,200 | 30.0 |
| 9,600 | 40.0 |
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
- Power (watts)
- A number, between 0 and 10000000, starting at 4,800.
- Voltage (V)
- A number, between 0 and 1000000, starting at 240.
- Phase
- Choose from Single phase, Three phase.
- Power factor
- A number, between 0 and 1, starting at 1.
- Load type
- Choose from Non-continuous, Continuous (3+ hours).
What the results tell you
| Result | What it is |
|---|---|
| Current | The headline result. A decimal figure. |
| Current for sizing | A decimal figure. |
| Suggested breaker | A category or planning selection, rather than a measured quantity. |
| Power in kW | A decimal figure. |
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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