How Many LED Strips Can One Power Supply Run? A Worked Calculator Guide

The three-step calculation

Step 1: power per reel = watts per metre × metres per reel. Step 2: total installed load = power per reel × number of reels, adding any other load on the output. Step 3: choose a suitable supply whose continuous rated output and operating conditions cover that total.

For an optional 80% planning target, calculate usable capacity = driver rated watts × 0.8; then divide by watts per reel and round down. Equivalently, divide the installed load by 0.8 to estimate a supply rating. Multiplying load by 1.2 is a different calculation: it gives only 16.7% unused capacity at the resulting rating, not a true 20% spare capacity.

Example: 200W driver with 24V, 15W/m strip

One 5m reel uses 5 × 15 = 75W nominal. A 200W, 24V supply offers 160W under an 80% planning target. 160 ÷ 75 = 2.13, so it accommodates two complete reels on that basis: 150W total and 50W remaining relative to the nameplate rating.

At 24V, two reels draw approximately 150 ÷ 24 = 6.25A combined. The driver output must be rated for that current; each 75W branch draws about 3.13A, so its own cable, fuse or protection arrangement where required, connector and controller also need appropriate ratings. Three reels draw 225W even before headroom and exceed the 200W rating.

Example: 12V strips on a 100W supply

Suppose a 12V strip is rated at 10W/m and you plan 2m per branch. Each branch uses 20W. Four branches use 80W, exactly 80% of a 100W supply; a fifth would reach the full 100W nameplate rating and exceed that planning target.

The four branches draw approximately 80 ÷ 12 = 6.67A combined. Because current is higher at a lower voltage for the same wattage, distribution cables and voltage drop deserve particular attention.

Power capacity is not maximum strip length

A 200W supply may have enough capacity for two 75W reels, but that does not mean a 10m end-to-end strip is permitted. Copper tracks and interconnections have their own limits. Feed each reel in the arrangement allowed by the strip maker, often as separate parallel branches.

For long installation runs, calculate voltage drop along the feed cable and the strip itself. A high-capacity central supply cannot guarantee that the farthest LEDs receive their rated voltage. Split feeds or add injection points where the product instructions permit.

Cases that change the answer

Different strip models can share a suitable supply if they require the same fixed voltage and the combined load is properly calculated. A single controller may limit current more than the supply does. An enclosed, hot or outdoor position may also reduce a driver’s allowed output under its temperature derating curve.

For RGB, tunable-white or addressable strips, use the rated maximum consumption of all channels or pixels that could be on simultaneously, and check the controller and power-injection instructions. Do not estimate from a dimmed appearance.

Final sizing checklist

Before placing an order, note the following values for every branch.

• Exact strip voltage and watts per metre from the current datasheet.
• Metres in each run, number of runs and calculated total watts.
• Total amps at supply voltage and amps through each cable and controller output.
• Driver continuous rating, headroom decision and temperature derating.
• Maximum feed length, voltage drop, IP protection and accessible distribution points.