Everyday
Christmas Light Calculator
Enter your roofline, tree, windows, doors and shrubs, pick a bulb type and style, and the page works out how many bulbs and strands the whole house takes, what the load is in amps and circuits, and what the season costs.
How it works
Behind the numbers
Each section gets its own bulb count. Roofline feet multiply by bulbs per foot, which is 1 for C9 and 2 for mini. Windows count as 15 feet of outline each and doors as 20 feet, times the same bulbs per foot. A tree counts as 100 mini lights per foot of height, or 50 per foot for C9, since the larger bulbs sit farther apart. Each shrub net counts as 100 lights, the usual count for a 4 by 6 foot net.
Bulbs turn into strands by division, rounded up. A C9 strand holds 25 bulbs and a mini strand holds 100, so the default house at 810 LED C9 bulbs needs 33 strands. Watts follow from watts per bulb: 1.0 for LED C9, 0.07 for LED mini, 7 for incandescent C9 and 0.4 for incandescent mini. Amps are watts divided by 120, and circuits divide amps by 12, the usable share of a 15 amp outdoor circuit under the 80 percent rule for continuous loads.
Cost has two parts. Strand cost is strands times your price per strand. Power cost is watts times hours per day times days in the season, divided by 1000 for kilowatt hours, times your rate. The default house costs $396 in strands and $33.05 in power for the season. Swap the bulb type to incandescent C9 and the same house draws 47.25 amps and needs 4 circuits, which is the clearest reason the page shows both numbers side by side.
FAQ
Questions, answered
How many Christmas lights do I need for my house?
Count by section, not by one rule. A house with 60 feet of roofline, a 7 foot tree, 4 windows, 2 doors and 3 shrub nets takes 810 LED C9 bulbs: 60 for the roofline, 350 for the tree, 60 for windows, 40 for doors and 300 for shrubs. That is 33 strands. Enter your own sections and the page counts each one for you.
How many lights per foot of Christmas tree?
The usual planning figure is 100 mini lights per foot of tree height, so a 7 foot tree takes 700 mini lights. C9 bulbs are larger and sit farther apart, so the same tree takes about 50 C9 bulbs per foot, or 350 in total. These are planning figures: a sparsely decorated tree takes fewer, a fully wrapped one takes more.
How many amps do Christmas lights draw?
Divide total watts by 120. The default house at 810 LED C9 bulbs draws 810 watts, or 6.75 amps, which fits one circuit. The same house with incandescent C9 bulbs draws 5,670 watts, or 47.25 amps, which needs 4 circuits at 12 usable amps each. That gap is why LED strands are the usual choice for a whole house.
How many strands can I plug into one outlet?
Stay under 12 amps of continuous load on a standard 15 amp outdoor circuit. LED mini strands draw very little, so dozens can share a circuit. Incandescent C9 strands draw 175 watts each at 25 bulbs, so 8 strands already pass 12 amps. The page totals your amps and circuits so you can split strands across outlets before you hang anything.
How much does it cost to run Christmas lights for a season?
Two costs add up: strands and power. The default house costs $396 in strands at $12 each, plus $33.05 in power for 810 watts running 6 hours a day for 40 days at 17 cents per kilowatt hour. Power is the smaller share with LEDs. With incandescent bulbs the same house costs far more in power, which is worth checking before you buy.