How many Christmas lights?
Measure your run, railing or tree. Get an estimate you can save to your plan.
Three examples, with the working shown.
A straight 48 ft run
48 ÷ 25 ft of illuminated length per set = 1.92. Round up to 2 sets supplying 50 ft. Plan a suitable route for the extra 2 ft, or choose a better combination of lengths. The lead to the outlet is separate.
A 6 ft railing, wrapped
With a 12 in circumference and a 6 in advance per turn, light length = 6 × √(1 + (12 ÷ 6)²) = about 13.4 ft. This is an ideal spiral on a constant-size rail. Add the actual lead routes and any detours around supports.
A 7.5 ft tree
7.5 × 100 mini lights per foot = 750 lights. In 100-light sets, eight sets supply 800 lights. A wider tree or denser effect can need more; trial a section first.
Tree-light starting point: Christmas Light Source: tree-light estimating guide. Checked September 16, 2026.
Before you use the estimate
This estimates quantity, not electrical capacity, mounting requirements or the permitted number of connected sets. Follow the exact model’s labels and instructions. Do not cut finished strings or connect every calculated set end to end unless the system explicitly allows it.
For branches, irregular posts or deep swags, trace the actual route with string and use that measured length in straight-run mode. Imperial units are used here: 12 inches = 1 foot; 3 feet = 1 yard.