Power Supply Calculator

Estimate what size DC power supply you may need for low-voltage devices, LED strips, routers, cameras, controllers, pumps, motors, and small workshop projects.

Enter Your Numbers


Presets are rough examples. Use the actual device label or manual when possible.


Examples: 5V, 12V, 24V, 48V.


Use amps from the device label, manual, or measured load.


Use the number of devices powered by the same supply.


Use 1.0 for steady loads. Motors and pumps may need 1.5–3x or more.


Adds headroom so the power supply is not running at its limit.


Use 100% unless you know the load will usually run lower.


Your Results

Suggested supply current

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Enter values and calculate.

Suggested supply watts

—
Power supply watt rating estimate.

Base load

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Before surge and buffer.

Common size

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Rounded up to a common rating.

This calculator gives a planning estimate only. Check the device label, power supply rating, connector rating, wire size, voltage drop, heat, enclosure ventilation, and manufacturer instructions.

How to Use This Power Supply Calculator

Enter the output voltage your device needs, the current draw per device, and how many devices the power supply will run. Then add a startup multiplier and planning buffer.

This calculator is mainly for low-voltage DC power supplies. It is not for sizing household circuits, breaker panels, permanent wiring, or code-sensitive electrical work.

Formula Used

Base amps = current per device × number of devices × load level
Surge-adjusted amps = base amps × startup multiplier
Suggested amps = surge-adjusted amps × (1 + buffer %)
Suggested watts = suggested amps × voltage

Example Calculation

A 12V device that draws 5 amps has a base load of:

12V × 5A = 60 watts

If you add a 1.2x startup multiplier and a 25% planning buffer, the suggested supply size becomes about 7.5 amps, or 90 watts.

Common Power Supply Sizing Mistakes

  • Choosing a power supply with the correct voltage but too little current.
  • Running a power supply at its maximum rating for long periods.
  • Ignoring motor startup current, pump startup current, or LED strip voltage drop.
  • Using thin wires or weak connectors with high-current low-voltage loads.
  • Mixing devices that need different voltages on the same supply.
  • Ignoring heat and ventilation around enclosed power supplies.

Important Safety Note

Use this calculator as a planning tool only. Do not use it as permission to overload a power supply, wire, connector, fuse, battery, controller, outlet, extension cord, or electrical system.

For mains wiring, permanent circuits, damaged power supplies, sparks, heat, burning smells, exposed conductors, or anything code-sensitive, stop and contact a qualified professional.