How Many Christmas Lights Do I Need? Tree, Roofline & Circuit Load
The short answer for a tree is 100 lights for every foot of height: 700 lights for a 7 ft tree, or about 7 strands of 100. For a roofline it depends on the length: about one 25 ft strand for every 22 ft of roof, with a little spare. This guide gives you charts for both, and explains how to avoid overloading a circuit, the one mistake that can ruin the holidays.
How many lights for a Christmas tree?
The standard rule is 100 lights per vertical foot of tree. Use fewer for a subtle look, and more for a showpiece. The numbers below show lights (and strands of 100) at four levels of fullness.
| Tree height | 50 per foot | 100 per foot (standard) | 150 per foot | 200 per foot |
|---|---|---|---|---|
| 4.5 ft | 225 (3 strands) | 450 (5 strands) | 675 (7 strands) | 900 (9 strands) |
| 5 ft | 250 (3 strands) | 500 (5 strands) | 750 (8 strands) | 1000 (10 strands) |
| 6 ft | 300 (3 strands) | 600 (6 strands) | 900 (9 strands) | 1200 (12 strands) |
| 6.5 ft | 325 (4 strands) | 650 (7 strands) | 975 (10 strands) | 1300 (13 strands) |
| 7 ft | 350 (4 strands) | 700 (7 strands) | 1050 (11 strands) | 1400 (14 strands) |
| 7.5 ft | 375 (4 strands) | 750 (8 strands) | 1125 (12 strands) | 1500 (15 strands) |
| 8 ft | 400 (4 strands) | 800 (8 strands) | 1200 (12 strands) | 1600 (16 strands) |
| 9 ft | 450 (5 strands) | 900 (9 strands) | 1350 (14 strands) | 1800 (18 strands) |
| 10 ft | 500 (5 strands) | 1000 (10 strands) | 1500 (15 strands) | 2000 (20 strands) |
| 12 ft | 600 (6 strands) | 1200 (12 strands) | 1800 (18 strands) | 2400 (24 strands) |
Rather than joining ten strands of 100 together, buy fewer, longer strands (300 or 400 lights) for a big tree: it means fewer connections and fewer plugs. The Christmas tree lights calculator does the sums for any height, and checks the tree fits under your ceiling.
Choosing the tree height
Leave room for the stand (a few inches) and the topper (a foot or so). As a guide, a tree should be 1 to 1½ ft shorter than the ceiling:
| Ceiling height | Tree height |
|---|---|
| 8 ft | 6½ to 7 ft |
| 9 ft | 7½ to 8 ft |
| 10 ft | 8½ to 9 ft |
| 12 ft | 10½ to 11 ft |
How many lights for a roofline?
Outdoor lights follow the shape of the house, so you start by measuring the length of every edge you want to outline. Add 10% for corners and spares, divide by the length of a strand, and round up. Bulb counts depend on the spacing: C7 and C9 bulbs are usually 12 inches apart, and mini lights 4 inches.
| Length to outline | 25 ft strands (with 10% spare) | C9 bulbs (12 in apart) | Mini lights (4 in apart) |
|---|---|---|---|
| 40 ft | 2 strands | 44 bulbs | 132 bulbs |
| 60 ft | 3 strands | 66 bulbs | 198 bulbs |
| 80 ft | 4 strands | 88 bulbs | 264 bulbs |
| 100 ft | 5 strands | 110 bulbs | 330 bulbs |
| 150 ft | 7 strands | 165 bulbs | 495 bulbs |
| 200 ft | 9 strands | 220 bulbs | 660 bulbs |
The outdoor lights calculator also counts clips (one per bulb) and the extension cord to reach the outlet. Measure from the ground with a laser measure, or from a photo with a known reference, rather than climbing the roof.
How many strands can one outlet run?
This is where people get into trouble. A circuit is limited by its breaker: a 15 amp circuit at 120 volts supplies 1,800 watts, but anything that runs for hours should stay under 80% of that, 1,440 watts. A 20 amp circuit allows 1,920 watts. The number of strands you can run is the safe wattage divided by the watts per strand:
| Type of strand | Watts | Max on a 15 A circuit | Max on a 20 A circuit |
|---|---|---|---|
| LED mini, 100 lights | 5 W | 288 | 384 |
| Incandescent mini, 100 lights | 40 W | 36 | 48 |
| LED C9, 25 lights | 5 W | 288 | 384 |
| Incandescent C9, 25 bulbs | 175 W | 8 | 10 |
Those are estimates: check the watts printed on your own package. And remember that other things share the circuit: inflatables, a freezer in the garage, and so on. The circuit load calculator subtracts anything else on the breaker, and suggests an extension cord gauge.
There is a second limit on the package: the maximum number of strands you can connect end to end. It is set by the thin wire inside each strand, and is often just 3 for old-style incandescent mini lights, but dozens for LED. Follow whichever limit is lower.
Why LED is worth it
- Power: an LED strand uses roughly a tenth of the power of an incandescent one, so a whole house of lights costs pennies to run, and one outlet can handle all of it.
- Heat: LEDs stay cool, which cuts the fire risk on dry trees.
- Life: LEDs last for thousands of hours and resist breakage, so they pay for themselves over several seasons.
- Looks: modern LEDs come in warm white that closely matches the classic incandescent glow.
Safety checklist
- Use lights rated for where you are putting them: indoor, outdoor or both. The tag will say.
- Plug outdoor lights into a GFCI outlet, with outdoor-rated extension cords. Keep connections off the ground and out of puddles and snow.
- Check each strand for cracked sockets, bare wire and loose connections before hanging, and throw away any that are damaged.
- Water a real tree every day, and turn the lights off when you go to bed or leave the house. A timer makes it easy.
- Do not run cords under rugs, through closed doors or windows, or where they will be walked on.
- Use a stable ladder, have someone hold it, and never work near power lines.
A shopping plan
- Measure the tree, roofline, windows, railings and any other places you want lights.
- Use the calculators above to work out the strands, bulbs and clips for each.
- Check the watts and maximum connected strands on each product.
- Buy cords and timers rated for outdoor use, and count the outlets you will need.
- Test everything on the ground before you hang it. Buy early: popular lights and cords sell out as the season gets closer.
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.