Christmas Lights Calculator
For 150 ft of roofline you need about 7 strands of 25 ft C9 LED lights (175 ft, which includes 5% spare), 165 clips and 3 outdoor cords. That is about $189 in materials and $1 of electricity for the season.
Enter your own roofline below. The list updates as you type and prints from the page.
Your estimate appears here
Enter your roofline in feet to see an installed price range with every line shown. No account, no email.
Not sure of your roofline? Open “Estimate from house size”, or .
How the counts are worked out
Roofline feet are multiplied by 1.05 so the last strand reaches the corner, then divided by the length of one strand and rounded up. Clips are one per foot for C9 bulbs, more for mini and icicle lights, with 10% spare because some always break or go missing. Extension cords are one per 60 ft of run, and the number of timers follows the cords and the total wattage so no timer is overloaded.
| Light type | Strand length | Lights | Clips per ft | Price per strand |
|---|---|---|---|---|
| C9 LED bulbs | 25 ft | 25 | 1 | $14 |
| Mini LED lights | 33 ft | 100 | 1.2 | $7 |
| Icicle LED lights | 10 ft | 100 | 2 | $9 |
How to measure your roofline
- List the edges you want lit: front eave, side eaves, gable edges, ridge line, garage.
- Measure each edge from the ground with a tape or measuring wheel, or read it off a satellite map, and add them up.
- Round up and enter the total. For a gable, measure along the sloped edge, not the base.
You can also split the roofline into zones, up to 2 on the free plan, to keep each run's length next to its name.
What the lights cost to run
Electricity cost is watts times hours times days, divided by 1,000, times your price per kWh. For the 150 ft example, LEDs draw about 35 W with the two trees left out and use 7.35 kWh over 35 nights at 6 hours, about $1. Incandescent C9 bulbs on the same roofline draw about 1225 W and cost about $44.
| Product | LED | Incandescent |
|---|---|---|
| C9 strand, 25 bulbs | 5 W | 175 W |
| Mini strand, 100 lights | 4.8 W | 40 W |
| Icicle strand, 100 lights | 7 W | 45 W |
| Net lights, 150 lights | 7 W | 60 W |
| Small strand, 50 lights | 2.4 W | 20 W |
About 17 cents per kWh is a rough US residential average for 2025. Your bill has your real rate.
Shopping tips
- Buy one extra strand of every length. Matching a bulb color next week is harder than it sounds.
- Use outdoor-rated cords and timers only, and check the maximum number of strands that can be connected end to end on the package.
- Test every strand on the ground before it goes on the roof.
- If a quote from an installer is on your mind, compare it with the installation cost guide.
Questions
How many Christmas lights do I need for my roofline?
Divide your roofline in feet by the length of one strand and add about 5% spare. For 150 ft of 25 ft C9 strands that is 7 strands.
How many clips do I need?
About one clip per foot for C9 bulbs, 1.2 per foot for mini lights and 2 per foot for icicle lights, plus 10% spare.
How much electricity do Christmas lights use?
LED strands use a few watts each. The 150 ft LED example costs about $1 to run for 35 nights; incandescent C9 bulbs cost about $44.
How many extension cords and timers do I need?
One outdoor cord per 60 ft of run is a good start, and one timer per two cords, more if the total load is high.
Is the calculator free?
Yes. Every estimate, the line-by-line breakdown, the DIY shopping list on screen and the tree light calculator are free, with no account. A free one-page summary PDF is included. The Lighting Plan PDF ($2.99, one time) adds the house layout by zones, a shopping list PDF, a quote comparison worksheet and an electricity budget.
How accurate is this estimate?
It is a model built on typical 2025-2026 US price ranges, so treat it as a planning number, not a quote. Real prices depend on the installer, how hard your roof is to work on, the lights, and your local market. Get at least three quotes and use the range here to spot offers that are far off.