Calculate an LED strip total LED count, wattage, and the power supply size you need.
Voltage drop & injection
Cut points & color
Usage Tip
Keep single runs under about 5 meters for 12V strips; longer runs need power injected at both ends to avoid dimming.
total watts = meters × watts per meter
power supply ≥ total watts × 1.2
Size the power supply at the recommended minimum or the next size up.
Sizing an LED strip run
An LED strip install comes down to three numbers: how much power the strip draws, how big a driver it needs, and how far it can run before the far end goes dim. The load is simply the length times the watts per foot. The driver should be that load plus a margin. And the maximum run before you need to feed power partway along depends on the voltage — low-voltage 5V and 12V strips fade much sooner than 24V or 48V. This calculator works all three out, and tells you where to inject power so the strip glows evenly end to end.
Watts per foot and total load
The total draw is the length times the strip's rated watts per foot:
Total watts = length × watts per foot
A 24 ft run of 6 W/ft strip draws 144 watts. Strips are sold both ways — watts per foot and watts per meter — so watch the units. Common ratings: 4.4 W/ft equals 14.4 W/m, and 5.9 W/ft equals 19.2 W/m.
LED strip length chart
Typical maximum single run before the voltage drops enough to dim the far end and you need power injection:
| Voltage | Typical max run |
|---|---|
| 5V | 6 to 10 ft |
| 12V | 16 to 20 ft |
| 24V | 32 to 40 ft |
| 48V | 50 ft and up |
Higher voltage carries power further for the same current, which is why 24V is the sweet spot for most rooms and 48V is appearing for long architectural runs.
Driver headroom
Never load a driver to its full rating. Size it about 20 to 25 percent above the strip load so it runs cool and lasts. An 80W strip load wants a 100W driver; a 144W load wants a 180W driver. This margin also covers the inrush when the strip switches on.
Power injection
On a long low-voltage run, the end is dimmer and warmer-looking than the start because the voltage sags along the copper. Power injection means feeding the supply voltage to more than one point on the strip — both ends, or every so many feet — so the whole run sees full voltage. A 12V strip past about 16 ft, or a 5V strip past about 6 ft, almost always needs it. Feeding both ends roughly doubles the usable length; injecting at intervals extends it further.
RGB and RGBW strips
Color strips draw the most at full white, when every channel is on at once. An RGBW strip can pull noticeably more than its single-color rating, so size the driver for the full-white load, not the per-color figure. If the spec sheet lists a per-channel wattage, add them up.
Cut points
LED strips can only be cut at marked points, usually shown by a scissors icon and copper pads, spaced every few inches depending on the strip. Cutting elsewhere kills the segment past the cut. Check the cut spacing before planning an exact length, and round your run to land on a cut line. The copper pads are also where you solder or clip the next connector or injection feed.
Frequently asked questions
How many feet of LED strip can I run?
Roughly 16 ft for 12V and 32 ft for 24V before the end dims. Beyond that, inject power at both ends or at intervals.
What size power supply for LED strips?
Take the length times watts per foot, then add 20 to 25 percent. A 144W load wants about a 180W driver.
Why is the end of my LED strip dimmer?
Voltage drop along the run. The fix is power injection — feeding the supply voltage to the far end as well.
Can I cut LED strip to any length?
Only at the marked cut points, spaced every few inches. Cutting between them disables that section.
Is 24V better than 12V for LED strip?
For longer runs, yes — 24V carries power about twice as far before needing injection, for the same brightness.
How do I calculate amps for an LED strip?
Amps equal total watts divided by voltage. A 144W strip at 24V draws 6 amps.
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Estimates are for planning. Actual watts per foot, maximum run and cut spacing vary by strip — always check the product spec sheet. Use a driver and wiring rated for the load, follow the manufacturer's instructions, and have mains-voltage connections done by a qualified person where required.