Choosing the right size power supply for LED Strip
12w, 5w, 30w per metre? - all LED Strips will be given a quoted power consumption and the idea is that you should multiply this by the number of metres to find the required size of the power supply and whilst this is broadly correct there are some other factors to consider.
1 For long term reliability, always choose a power supply which has around 30% more power than you need - ie if you need 75w of power then choose a 100w power supply.
2 The rated power of an LED Strip will always be calculated using a very short piece of LED Strip - probably 0.5m, however when you use longer lengths the actual power per metre begins to fall so, for example, a 10m length of 12w rated led strip might only require a maximum of 90w of power in total and not 120w - this means you may be able to specify a smaller, less expensive power supply with no impact on reliability and performance.
RGBW LED Strip Power Ratings. The issue of real power consumption is more complex with RGBW as manufacturer power ratings are based on worst case scenarios which in reality are difficult to use. The most power hungry combination is to use full yellow alongside full power white, if you use any other combination then the actual power consumption will be significantly less.
This means that for our 96 LED RGBW LED Strip a10m run which has a nominal power consumption of 300w to which you should ordinarily add some "headroom" could mean you specify a 350w power supply when in reality a 240w will be fine given the natural voltage drop and the fact that there is practically no chance of you ever using the maximum power colour combinations.
To help with this, we have physically measured our strips for real power consumption and crated a calculation tool which will recommend the correct, safe power supply for the actual length of LED Strip you wish to use.