To measure for Christmas lights, you'll need to determine the length of the space you want to cover and the amount of light strands you'll need to get the job done. Start by measuring the length of the area you want to illuminate. Then, divide that length by the length of the light strand you plan to use. This will give you the number of strands you need to fully cover the area. Finally, add a few extra strands to account for any unexpected twists or turns in the lighting design.