Power Supply Current Calculator
Estimate power-supply output current, converter input current, or a recommended current rating with design margin. Use it for adapter selection, DC/DC source sizing, wiring review, and early system power budgeting.
Engineering tool
Power Supply Current Calculator
Calculate source or load current and apply engineering margin when selecting a power supply.
Result console
- Output current
- 5A
- Output power
- 60W
Formula: Iout = Pout / Vout
Use the calculated current as the nominal DC load estimate, then account for startup, transient, and environmental derating.
Formula reference
Power Supply Current Formulas
Efficiency is entered as a percentage and converted to a decimal for calculation.
Output current: Iout = Pout / VoutInput power: Pin = Pout / efficiencyInput current: Iin = Pin / VinRecommended rating: Irated = Iload × (1 + margin)Variable definitions
- Pout and Pin
- output and input power
- Vout and Vin
- output and input voltage
- Iload
- worst-case load current
- Margin
- additional current capacity as a decimal
Worked Examples
Output Current
60 W / 12 V = 5 A.
Input Current
60 W / 90% / 24 V ≈ 2.778 A.
Recommended Rating
5 A × 1.25 = 6.25 A.
Engineering Notes
- Power supplies should be sized above expected load current.
- Efficiency affects input current and thermal load.
- Startup surge and transient loads may require additional current margin.
- Continuous current rating should be checked at ambient temperature.
- Use worst-case voltage and load conditions for reliable design.
Support reference
FAQ
How do you calculate power supply current?
For a DC output, divide output power by output voltage. For converter input current, first divide output power by efficiency, then divide input power by input voltage.
How much current should my power supply have?
Choose a continuous current rating above the worst-case load. A 25% margin is a useful starting point, with more allowance for surge or strongly dynamic loads.
Why does efficiency affect input current?
A converter draws more input power than it delivers because some energy becomes heat. Lower efficiency therefore increases input power and current for the same output load.
How much safety margin should I add?
Twenty-five percent is a common screening value. Startup surge, ambient temperature, supply derating, cable loss, and load uncertainty may require more.
What is the difference between input current and output current?
Input current is drawn from the source at the input voltage. Output current is delivered to the load at the output voltage; conversion ratio and efficiency make them different.
Documentation
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