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LED Strip Power Supply Calculator

Work out the right power supply size and current for your LED strip installation.

How it is calculated

The total load of the strip is total W = length × W per metre, with length in metres and the power rating in watts per metre taken from the strip's label. The recommended power supply is that total plus a fixed 20% margin: PSU W = total × 1.2. The current the strip draws is amps = total W ÷ supply voltage.

Supply voltage is in volts; if you leave it empty or enter zero or a negative number, the tool assumes 12 V. Length and watts per metre must be above zero. Watts, amps and the supply wattage are shown to one decimal. The current is based on the strip's own load, not on the supply rating. The tool does not check voltage drop along a long run, so very long strips may still need to be split or fed from both ends even if the total wattage looks fine.

Worked example

A 5 m strip is rated at 14.4 W per metre and runs on a 12 V supply. The total load is 5 × 14.4 = 72.0 W. Adding the 20% margin gives a recommended supply of 72 × 1.2 = 86.4 W, so in practice you would buy a 100 W unit. The strip draws 72 ÷ 12 = 6.0 A. On a 24 V supply the same strip would draw 3.0 A, with the same 72 W load and the same 86.4 W supply size.

Try this example →

Common mistakes

  • Entering the length in centimetres or feet. The field is metres, so a 500 cm strip is 5.
  • Using the strip's total wattage as the W per metre value. The field expects watts per metre; entering 72 for a 5 m strip gives 360 W.
  • Leaving the voltage out for a 24 V strip. A blank voltage defaults to 12 V, which doubles the current shown.
  • Buying a supply rated exactly at the total load. The extra 20% is the allowance for continuous running, so use the PSU line rather than the total.
  • Assuming a long run is fine because the wattage fits. Voltage drop along a single long strip is not checked here.

About this calculator

This calculator sizes an LED strip's power supply from the strip's length and its rated power draw per meter: total load = length × W/m, and current = watts / supply voltage (typically 12V or 24V; 12V is assumed if you leave it blank). To keep the supply from running at its thermal limit continuously, the calculator adds 20% headroom above the calculated load — the same kind of margin electricians build in for any continuous-duty circuit, since running a supply at 100% of rated capacity shortens its lifespan and risks overheating.

DIY installers wiring under-cabinet kitchen lighting, cove lighting, or accent strips use this to avoid undersized transformers that dim, flicker, or fail early. It does not check voltage drop, so for a long run, remember that it may need to be split or fed from both ends to avoid dimming along the strip.

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Comments (1)

  • Editorial team

    Voltage does not change the wattage, only the current. A 10 m strip at 9.6 W per metre is 96.0 W in total either way, and the tool suggests a 115.2 W supply. It draws 8.0 A at 12 V but 4.0 A at 24 V, so a 24 V strip lets you use thinner wire for the same power. Leaving the voltage blank means 12 V is assumed. What strip length and voltage are you planning?

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