Enter the length, the voltage and the power per metre of your LED strip. The calculator gives the total power, a power supply with 20 % headroom, the current, the number of feed points and the voltage drop over the cable. A 24 V strip of 10 W per metre, 4.2 m long, needs a 60 W power supply and, with 3 m of 0.75 mm² cable, loses about 1 % of its voltage.
What does this calculator work out?
Everything you need to know to order an LED strip with the right parts: the total power, the power supply you need, the current that flows through the cables, at how many points you need to feed the strip, how much voltage is lost over the cable to the strip, and how much light the strip gives in total. For worktop lighting, the tool also estimates how many lux reach the worktop.
How to choose a strip, with colour temperature, IP rating and profile, is explained in choosing an LED strip.
How does the tool calculate?
- Power = watts per metre × length.
- Power supply = power × 1.2, rounded up to the next common size: 30, 40, 60, 75, 100, 150, 200, 240 or 320 W. Above 320 W, the tool suggests several power supplies.
- Current = power ÷ voltage.
- Feed points = length ÷ maximum length per feed point, rounded up.
- Voltage drop over the cable = 2 × cable length × current per feed point × resistance per metre. The factor 2 is for the wire there and back. For a percentage, divide by the voltage.
- Luminous flux = lumens per metre × length. For worktop lighting, the tool estimates the lux on the worktop as lumens per metre × 0.5 ÷ the depth of the worktop.
What assumptions does the tool use?
- 20 % headroom on the power supply. Power supply manufacturer Mean Well lets its LED drivers run at full power as long as the temperature stays within the specifications. The headroom covers the tolerance on the power of the strip, the heat in a small space and a later extension.
- Maximum length per feed point. By default 5 m for 24 V, as LEDVANCE states for its 24V COB strip with a short supply cable, and a cautious 3 m for 12 V. If the datasheet of your strip gives a different value, enter that one.
- Cable resistance according to IEC 60228 for flexible copper wire at 20 °C: 0.039 Ω per metre for 0.5 mm², 0.026 for 0.75 mm², 0.0195 for 1.0 mm², 0.0133 for 1.5 mm² and 0.008 for 2.5 mm².
- Limit for the cable. Above 3 % loss, the tool suggests a thicker cable, a shorter cable or 24 V. That is a rule of thumb from practice.
- Light output. If you do not know the lumens per metre, the tool works with 100 lumens per watt.
- The strip itself. The tool does not calculate the loss in the copper tracks of the strip; that is what the maximum length per feed point from the datasheet is for.
Frequently asked questions
Can one power supply feed several strips?
Yes, if they have the same voltage and their combined power stays within the capacity of the power supply. Connect them in parallel, each with its own cable to the power supply, instead of linking them one after the other.
Does the power supply have to be dimmable?
Only if you want to dim with an ordinary dimmer or with DALI. If you use a controller between the power supply and the strip, with a remote control or an app, an ordinary constant-voltage power supply will do. See dimming LED bulbs.
Why does the tool give a different power supply than the sum in watts?
Because it takes 20 % headroom and rounds up to a size you can buy. A 42 W strip therefore gets a 60 W power supply.
What if my cable is longer than 10 m?
Then the loss rises quickly. Place the power supply closer to the strip, or use a thicker cable. For 24 V with a few amps, 1.5 mm² is a safe choice for long cables.
Sources
- Neu im LED Strip System: LEDVANCE COB LED Strip (tabel met voedingslengtes), LEDVANCE (2021)
- Conductor resistance volgens IEC 60228 / EN 60228, Bayka (geraadpleegd 2026)
- LED driver Q&A, MEAN WELL (geraadpleegd 2026)
