Christmas Light Strands Calculator
Find how many light strands you need for your roofline and trees, plus what the buy cost and holiday electricity bill will be.
How it works
Strands = ceil(length ÷ strand length) · Bulbs = strands × bulbs/strand · kWh = strands × watts ÷ 1000 × hours/day × days · Electricity = kWh × price
You size a light display by total length to cover, not by area — measure the roofline, any railings, and the wrap length of each tree, then divide by the length of one strand and round up. The running cost depends almost entirely on bulb technology: a 100-bulb mini-incandescent strand draws about 40 watts, while an equivalent LED strand draws only a few watts, so switching to LED can cut the seasonal electricity bill by 80–90%.
Worked example
To cover 150 ft with 25-ft strands you need ceil(150 ÷ 25) = 6 strands, or 600 bulbs. At $12 each that is $72 to buy. Running 6 × 40 W = 240 W for 6 hours a day over 30 days is 240 ÷ 1000 × 6 × 30 = 43.2 kWh, about $6.48 at $0.15/kWh.
Frequently asked questions
How many feet of lights do I need for my house?
Measure the full roofline you want outlined, add the length of any railings or columns, and for wrapped trees estimate the trunk or branch length you will spiral. Add those together — that total is the "length to cover" this calculator divides by your strand length.
Do LED lights really save money?
Yes. A 100-bulb incandescent strand uses roughly 40 watts; a comparable LED strand often uses under 5 watts. Over a month of daily use that difference is the gap between a few dollars and a fraction of a dollar per strand, and LEDs also run cool and last far longer.
How many strands can I safely connect end to end?
Follow the limit printed on the strand packaging — commonly around 3 to 5 incandescent strands or many more LED strands per run — because it is set by the wire gauge and the fuse rating, not by how many will physically plug together.
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This calculator is for educational purposes. Double-check important results before acting on them.