How to Size a Power Supply for 12V and 24V LED Strips

Knowing how to size a power supply for LED strips saves you from flicker, dim ends and burned-out drivers. LED strips are a daily job for electricians, sign shops and DIY installers, and most strip problems we hear about come from the power supply, not the strip.

The usual causes: a supply that is too small, set to the wrong voltage, or not built for where it is installed. This guide gives you a quick LED strip power supply calculator, then walks through five steps to choose a constant voltage (CV) power supply for 12V and 24V LED strips, with worked examples and MEAN WELL models you can order today.

LED strip power supply calculator: the quick formula

1. Total watts = strip power (W/ft) × total length (ft)
2. Minimum supply rating = total watts ÷ 0.8 (so the supply runs at about 80% load)
3. Current (A) = total watts ÷ strip voltage (12V or 24V)

Then choose a supply with the same output voltage as your strip and a rating at or above the number from line 2. The steps below explain each part.

Step 1: Confirm your strip is constant voltage

Look at the strip's label or spec sheet. If it is rated in volts (12V or 24V DC), it needs a constant voltage power supply. If it is rated in milliamps (for example 700mA or 1050mA), it needs a constant current driver instead. Not sure about the difference? Read our guide Constant Current vs. Constant Voltage LED Drivers.

The output voltage of the supply must match the strip exactly. A 24V strip on a 12V supply will be dim or won't light at all. A 12V strip on a 24V supply will overheat and fail.

Step 2: Find the strip's power rating

Strip manufacturers list power as watts per foot (W/ft) or watts per meter (W/m). Use the number from your strip's spec sheet, not a guess based on LED count. Keep in mind that a standard 5 m reel is 16.4 ft. To convert, multiply W/m by 0.3048 to get W/ft.

Step 3: Calculate the total load

Multiply the power rating by the total length you will connect to one supply:

Total watts = W/ft × total feet

To check the current, divide by the voltage: Amps = Watts ÷ Volts. You will need this number to size your wire and to compare it with the supply's rated current.

Step 4: Add headroom

A common rule of thumb is to load a power supply to no more than about 80% of its rating. That leaves margin for warm enclosures and keeps the supply running cooler over its life. So divide your total load by 0.8:

Minimum supply rating = Total watts ÷ 0.8

Also check the derating curve in the MEAN WELL datasheet if the supply will sit in a hot space, such as inside a ceiling, cabinet or sign box.

Example A: small 12V under-cabinet run

Say your 12V strip's spec sheet says 2.2 W/ft and you are installing 16.4 ft.

• Load: 2.2 × 16.4 = 36.1W (about 3A at 12V)
• With headroom: 36.1 ÷ 0.8 = 45W minimum
• Good fit: MEAN WELL LPV-60-12, rated 12V, 5A, 60W

Example B: 24V cove lighting, two reels

Say your 24V strip is rated 4.4 W/ft and you need 32.8 ft (two 5 m reels).

• Load: 4.4 × 32.8 = 144.3W (about 6A at 24V)
• With headroom: 144.3 ÷ 0.8 = 180W minimum
• Indoor fit: MEAN WELL LRS-200-24, rated 24V, 8.8A, 211.2W
• Outdoor or wet location fit: MEAN WELL HLG-240H-24A, rated 24V, 10A, 240W

Notice that a 150W class supply like the LRS-150-24 (156W) would technically carry 144W, but it would run at over 90% load. Sizing up is the safer choice.

Step 5: Pick the right type of supply for the location

Wattage is only half the decision. Where the supply is mounted matters just as much.

• Encapsulated, IP67 (LPV series): the LPV-60-12 and LPV-60-24 are fully encapsulated with IP67 protection and a 90–264VAC input. They are a simple choice for small runs, under-cabinet lighting and signage (see the LPV-60 datasheet).
• Enclosed, indoor (LRS series): the LRS series is a compact metal-case supply for use inside a fixture, cabinet or panel. It is not sealed, so keep it dry. On models like the LRS-200 and LRS-350, the AC input range is selected by a switch (90–132VAC or 180–264VAC), so set it to match your line voltage before powering up (see the LRS-200 datasheet). Our LRS selection guide covers this series in depth.
• Outdoor, high power (HLG series): the HLG-240H has a metal housing rated IP65 or IP67 (depending on type) and operates from −40 to +90°C case temperature. The A-type lets you fine-tune output voltage and current with a built-in potentiometer, and the B and AB types add 3-in-1 dimming (see the HLG-240H datasheet).

Quick reference: 12V and 24V LED strip power supplies by load

Ratings above are from the official MEAN WELL datasheets. Always confirm the full specs on the datasheet linked from each product page.

Don't forget voltage drop

Long strip runs lose voltage along their length, which shows up as dimmer or color-shifted LEDs at the far end. A few practical tips:

• Follow the strip manufacturer's maximum run length. For longer runs, feed the strip from both ends or split it into segments wired back to the supply.
• For the same wattage, 24V carries half the current of 12V, so 24V strips are usually the better choice for long runs.
• Size the wire between the supply and the strip for the full current and the distance, and follow local electrical code.

FAQ

Can I use a power supply that is bigger than I need?

Yes. A constant voltage supply only delivers the current the strip draws. A 240W supply on a 100W strip is fine, as long as the voltage matches.

Can I connect several strips to one power supply?

Yes. Wire them in parallel back to the supply and keep the combined load, plus headroom, within the supply's rating.

What size power supply do I need for a 16.4 ft (5 m) LED strip?

Multiply the strip's W/ft rating by 16.4, then divide by 0.8. For example, a strip rated 2.2 W/ft draws about 36W, so choose a supply rated at least 45W, such as the LPV-60-12 for a 12V strip.

Should I choose 12V or 24V strips?

For short runs either works. For longer runs or higher-power strips, 24V usually gives more even brightness because it needs less current for the same light output.

Are these power supplies dimmable?

The LPV and LRS series are not dimming drivers. The HLG-240H B and AB types offer 3-in-1 dimming (1–10VDC, 10V PWM signal or resistance), which adjusts the output current level. Dimming methods vary from strip to strip, so check with your strip manufacturer, or email us your setup and we will help you choose.

Related guides

• Constant Current vs. Constant Voltage LED Drivers: What Is the Difference?
• How to Choose a MEAN WELL LRS Power Supply
• How to Choose the Right MEAN WELL Power Supply for Your Application
• MEAN WELL Power Supplies: A Complete Buyer's Guide

Order today, ship today

Orders placed before 4:00 PM ship the same day, so you can get your project powered without waiting. Browse LED drivers and the LRS series at htdelectronics.com. Not sure which model fits your strip? Email your strip's voltage, W/ft and total length to sales@htdelectronics.com and we will help you pick the right MEAN WELL power supply.