How many landscape lights can I put on one transformer?

Dear Doing the Math,

The better way is to count watts, not fixtures. A 150-watt transformer can support fixtures whose combined wattage stays comfortably below 150 watts. Ten 5-watt LEDs and ten 12-watt fixtures are very different projects, even though both involve ten lights.

List each fixture's actual wattage, add the total, and leave headroom for startup behavior, future additions, and a transformer that is not asked to work flat-out every evening. The fixture-count guide explains a practical reserve instead of offering a magical fixture number.

Then look at where those lights will sit. A transformer can have plenty of total capacity while one long branch still struggles at the far end. Divide the system into logical branches, and check the longer runs for wire size and voltage drop. The transformer planner is a convenient place to see both the system total and the zone totals together.

If your count is close to the transformer's rating, do not treat that as a finish line. Choose the next size up or reduce the plan thoughtfully. A little spare capacity gives you options later, and it is much more pleasant than explaining to the next fixture that it arrived one watt too late.

— Ray