The wattage of an LED depends on how many lumens you need and how efficient the lamp is. Divide the lumens by the efficacy in lumens per watt to find the power. A lamp that must produce 800 lumens at an efficacy of 100 lumens per watt uses about 8 watts, which replaces an incandescent bulb of roughly 60 watts.

Efficacy varies between products, from around 60 or 70 lumens per watt for cheaper bulbs to more than 150 for the best fixtures. The driver uses some power as well, so the power drawn from the supply is a little higher than the power delivered to the LEDs. Check the rating on the package, which is for the whole product.

When you replace older lamps, match the lumens and not the watts, and check the color temperature and the beam angle too. Remember that a higher wattage LED also runs hotter, so make sure the fixture is rated for it, particularly in enclosed housings.