How to Calculate the Power Supply for LED Strips: Step-by-Step Guide with Examples

Knowing how to calculate the right LED power supply is the first step before buying any component. The question of which power supply I need for an LED strip depends on the wattage per metre, the length of the run, and the voltage of the strip.

This guide explains the process step by step with clear formulas and numerical examples so you arrive at the purchase with the figures in hand. Choosing the wrong LED strip power supply is the most common mistake. The strip, the profile, and the mounting may all be correct, but if the power supply is not sized properly it will cause flickering, overheating, or a shorter service life.

Why choosing the right power supply matters

The power supply regulates the current the strip receives. It is not a secondary component: it is what determines whether the installation runs stably over the long term.

A poor choice can sometimes take days to show up, as happened to an architecture student on his first work placement.

He installed COB LED strips in a shop window, calculated the strip and profile correctly, but bought the cheapest power supply he could find. Three days later, the window display started flickering. The power supply was too small and uncertified. He replaced it with a GXtronic unit with the correct headroom and the problem disappeared.

Consequences of an insufficient power supply

When the power supply operates at or above its capacity limit, the output voltage becomes unstable. This results in visible flickering, especially with high-density strips. On top of that, power supply overheating increases sharply.

Running continuously at 100% shortens the component's service life and can trigger the internal protection circuits or, in the worst case, cause an electrical fault. The undersized power supply for LED strip error is the most typical fault in domestic and commercial installations that need repair.

Why an oversized power supply is not ideal either

Going well above the required wattage has another cost: price and space. A 100W or 200W LED power supply takes up more room, weighs more, and costs more. If your installation needs 60W, a 200W power supply is money wasted. Reasonable oversizing means the 20% safety margin, not doubling or tripling the wattage.

Step 1 - Calculate the total wattage of your installation

The first figure you need is the total wattage the installation will consume. The formula is:

Total wattage (W) = Wattage per metre (W/m) × Total length (m)

To complete the sizing, it is also useful to know the output current in amperes. This is obtained by dividing the wattage by the voltage: I (A) = P (W) / V (V). A 100W power supply at 24V has an output current of 4.17A.

Wattage per metre by LED strip model

Each strip model has a wattage per metre specified by the manufacturer. The typical ranges are as follows:

Always check the data sheet for the specific model. The manufacturer's rated wattage is the reference figure; any generic estimate can lead to an incorrect calculation.

Practical example with 5 metres of COB strip at 12W/m

You have a 5-metre LED strip installation with a COB strip at 12W/m and 12V voltage.

Total wattage = 12 W/m × 5 m = 60W

That is the actual consumption of the strip. But that figure is not yet the wattage of the power supply you need. That is what Step 2 covers.

Step 2 - Apply the 20 per cent safety margin

Why the 20 per cent margin is essential

Power supplies should not run continuously at 100% of their capacity. The LED power supply safety margin of 20% acts as a thermal and electrical buffer. Without it, the power supply runs at its limit, runs hotter, and its service life is significantly reduced. This 20 per cent safety margin is standard practice in low-voltage electrical installations, not an optional recommendation.

Full calculation including the margin

Following the example above:

• Strip wattage: 60W
• 20% margin: 60 × 1.20 = 72W

The minimum recommended power supply for this installation is 75W or 100W (the next commercial size up). Never use a 60W power supply for a strip that consumes 60W.

To calculate the wattage of a power supply for an LED strip for any installation, the full formula is:

Power supply wattage (W) = Total strip wattage (W) × 1.20

The power supply calculation for 24V LED strips follows the same formula; the voltage does not change the calculation process, it only determines which power supply model to buy.

Step 3 - Choose the right voltage (12V vs 24V)

The 12V or 24V LED strip voltage determines which power supply you can use. They are not interchangeable: a 12V strip powered at 24V is damaged immediately.

When to use a 12V power supply and when to use 24V

For simple, short installations, 12V works well. For longer runs or high-density strips, a 24V power supply for LED strips is the safer option regardless of the wattage required.

When to use an LED driver for strips is a separate question. Drivers regulate constant current and are used with constant-current strips. Constant-voltage power supplies, on the other hand, are suitable for the vast majority of LED strips on the market.

If the project requires intensity control, a dimmable LED strip power supply with a 0-10V dimmable protocol allows brightness to be adjusted from an external controller. This option is available in both 12V and 24V within the GXtronic catalogue.

Voltage drop in long installations

Voltage drop over length is a factor that is frequently overlooked. In a 12V installation with 10 metres of strip, the difference in brightness between the start and the end of the run can be visible. With 24V, the drop is proportionally smaller. If the project exceeds 5 continuous metres, calculate the voltage drop or work directly with 24V and parallel strip connections from intermediate points.

Step 4 - Consider the installation environment

The environment determines the level of protection the power supply needs. This is shown as the IP rating in the product specifications.

IP20 power supplies for dry interiors

The IP20 power supply for dry interiors is the standard option for installations in plasterboard ceilings, furniture, or areas with no moisture or dust. It is the most common choice for decorative lighting projects in homes and retail premises. On the IP20 vs IP67 LED strip power supply question: using an IP20 unit outdoors or in wet areas is a real electrical hazard.

IP67 power supplies for outdoor or wet areas

When the installation is outdoors, in industrial kitchens, bathrooms, or any area where splashing is possible, the correct power supply is IP67. These units have a sealed enclosure and withstand moisture exposure without degrading. The price of an IP67 LED power supply per watt is higher, but there is no valid alternative when the environment demands it.

Most common mistakes when choosing a power supply

Connecting several strips in series without recalculating

A common mistake is connecting several LED strips to a single power supply without checking the total wattage. If you connect two 60W strips to a 100W power supply, the unit is overloaded.

How many metres of LED strip per power supply can a given unit handle? Divide its rated wattage by the strip's wattage per metre and apply the 20% margin. Parallel strip connection is the correct way to distribute the load when the installation has several runs.

Illustrative example: a 150W power supply with a 20% margin can feed up to 125W of actual strip consumption. If each metre consumes 10W, the maximum is 12.5 metres per power supply.

Ignoring certification and current ripple

TÜV LED power supply certification and other marks (CE, ENEC) guarantee that the unit has passed testing and that the ripple is within acceptable limits. An uncertified power supply may have high ripple, which causes flickering even when the wattage appears sufficient.

Overload and short-circuit protection is a basic requirement: if the strip develops a fault, a power supply without these protections can be damaged or become a hazard. LED power supply overload protection is a feature, not an extra.

Frequently asked questions about power supplies for LED strips

What happens if the power supply is insufficient for my LED strip?

The strip will receive less voltage than it needs. The most visible result is flickering, especially on start-up or after the installation has been running for a while. Over time, the power supply runs at its limit and can fail.

Can I connect several LED strips to the same power supply?

Yes, with conditions. The total wattage of all the strips must not exceed 80% of the power supply's capacity. Always use a parallel connection, not series. Calculate the total wattage before buying the power supply.

What is the difference between a 12V and a 24V power supply for LED strips?

The voltage must match that of the strip. The main practical difference is voltage drop over long runs. With 24V it is smaller, making it the recommended option for installations longer than 5 metres.

Why is my LED power supply getting hot?

Moderate power supply warming is normal. If the unit is hot to the touch, it is probably running above its capacity continuously or is installed in a space with insufficient ventilation. Check whether the installation wattage exceeds the recommended limit.

Do LED power supplies need maintenance?

They do not require active maintenance, but it is worth checking periodically that the ventilation in the space where they are installed is adequate. Accumulated heat is the main factor that shortens their service life.

What does the 20 per cent safety margin mean for LED power supplies?

It means the power supply should never run continuously at 100% of its rated wattage. By sizing the power supply with 20% additional headroom above the strip's actual consumption, you ensure it operates under optimal thermal and electrical conditions.

See the Icilux power supply catalogue and find the model with the voltage, wattage, and IP rating you need. If you have any questions about compatible COB or SMD LED strips, you will find those in the same section.