Calculate total wattage, current, and required power supply size for your LED strip installation
Choosing the right power supply is the single most common mistake in LED strip installations. Too small, and the strip dims or the supply overheats. Too large, and you waste money and rack space. This calculator removes the guesswork — enter your strip type, length, and voltage, and it will give you the exact wattage you need plus a recommended power supply size with headroom built in.
The basic math is simple: Total Power (W) = Strip Power per Meter × Length in Meters. A 5-meter strip rated at 14.4 W/m draws 72W continuous. But continuous is not the rating you size the power supply for — you always add headroom, typically 20-30%, so the supply is never running at 100% of its rated capacity. Running any power supply continuously at 100% load dramatically shortens its lifespan.
LED strips are rated by power per meter, and the number depends on the LED type, density (LEDs per meter), and brightness class. The most common consumer strips range from about 4.8 W/m for decorative accent lighting up to 24 W/m for premium COB strips used in professional installations.
| Strip type | Typical W/m | Use case |
|---|---|---|
| SMD 3528, 60 LED/m | 4.8 W/m | Decorative, low ambient light |
| SMD 5050, 60 LED/m | 14.4 W/m | Standard room or cabinet lighting |
| SMD 5050, 120 LED/m | 19.2 W/m | Bright task lighting |
| COB (continuous) | 14-24 W/m | Premium seamless light, no dots |
For any strip longer than 3-4 meters, 24V is almost always the better choice. The reason is voltage drop: as current flows along the thin copper traces in the strip, voltage falls off, and LEDs at the far end appear dimmer or change color. Because a 24V strip at the same wattage draws half the current of a 12V strip, it experiences roughly one quarter of the voltage drop over the same length.
Use 12V only for short runs (under 3 meters), low-power decorative strips, or when an existing 12V supply is available (RV, car, marine). For kitchen cabinets, coves, stairs, long accent runs, and any installation over 3 meters, specify 24V.
Voltage drop is not just a brightness issue — it changes the color temperature of white LEDs and shifts the hue of RGB strips. A strip that looks perfect near the power supply can appear noticeably yellow, dim, or off-color at the far end. The industry guideline is to keep voltage drop below 10% of the nominal voltage (so under 1.2V for a 12V strip, or 2.4V for 24V).
If your calculation shows excessive drop, there are three fixes: feed power to both ends of the strip (which halves the effective length), inject power at the midpoint with additional wires back to the supply, or step up to 24V to reduce current and drop. The advanced options below calculate drop based on strip length and help you decide which approach you need.
Never size a power supply for the exact calculated load. Good engineering practice is to pick a supply rated at least 20% above your load, for three reasons. First, cheap supplies often overstate their capacity — a "100W" no-name supply may only deliver 70W continuously. Second, running at full load continuously causes the supply to run hot and fail early, particularly the electrolytic capacitors which dry out with heat. Third, you may want to add more strip later, and headroom lets you do so without replacing the supply.
Brand matters. Mean Well, TDK-Lambda, and XP Power are industrial-grade names that deliver their rated power, filter the output properly (so LEDs do not flicker), and include overload/over-temperature protection. Generic supplies from marketplaces often skip these protections — they are fine for a quick test bench, but not for installations that need to last years inside a ceiling or wall.
It depends on the wattage rating of the strip. A standard 5050 strip at 14.4 W/m draws 72W over 5 meters, so you need a supply of at least 90W (72W plus 20% headroom). A 100W or 120W Mean Well LRS-100 or LRS-150 would be the typical choice.
Yes, if the total wattage of both strips plus 20% headroom is within the supply's rated output. For example, two 5-meter 14.4 W/m strips total 144W, so you would need at least a 175W supply, commonly rounded up to a 200W LRS-200.
This is voltage drop. It is normal for any strip longer than 3-4 meters on 12V, or 6-8 meters on 24V. The fix is to feed power to both ends of the strip, inject power at the midpoint, or switch to a higher-voltage strip to reduce current.
Yes. Supplies run continuously at 100% of rated load fail early due to heat stress on capacitors. A 20-30% headroom is standard engineering practice and significantly extends the lifespan of the supply. For installations that will run many hours daily, 30% is safer than 20%.
They work, but they often lack proper filtering (causing visible flicker on camera), overstate their power rating, and skip over-voltage/over-current protection. For a test bench or temporary setup they are fine. For permanent installations hidden inside a ceiling or wall, where a failure could start a fire, spend the extra on a Mean Well or equivalent branded supply with proper certifications.