The output wattage of each lighting transformer determines the number of lights it can power. To find the appropriate transformer for your project, you'll need to determine the wattage of your lights and calculate the minimum transformer size you'll need. When you browse our selection of transformers, you'll notice that they come in varying wattage levels. To determine the size of transformer you need, follow these simple steps: Determine the number of lights you want to connect to the transformer. Add up the wattage of each of these lights. Multiply the total wattage of all the lights by 1.1 to determine the minimum transformer size required. If your wattage requirements are particularly high, it may be a good idea to split your lighting between multiple transformers. For personalized assistance designing a lighting plan and selecting the right transformers, call our team at 1-800-990-7688. We're always happy to help our customers create a safe and bright lighting setup.