Christmas lights calculator
How many Christmas lights do I need?
Add each roof edge, tree and bush. The calculator turns them into bulb counts, strand counts and a shopping list priced from real catalog prices, so you buy the right amount the first time.
- Roofline edges
- Trees
- Bushes
- Shopping list
How the calculator works
Roofline edges
Every straight edge (an eave, a ridge, a flat fascia) is entered at its measured length. C9 bulbs sit in sockets molded into the wire, so the bulb count is feet × 12 ÷ spacing: 1 bulb per foot at 12 in., 0.8 per foot at 15 in. Each edge is treated as its own run with a male plug at the power end and a female plug at the other, and one clip holds each bulb to the gutter or shingle.
Gables and roof pitch
A gable end has two sloped edges (rakes) that meet at the peak. From the ground you can measure the width at the base; the pitch is the rise in inches per 12 in. of horizontal run, often printed on plans or measured with a level and tape. Each rake is (width ÷ 2) × √(1 + (pitch ÷ 12)²).
| Pitch | Factor | 24 ft. gable, both rakes |
|---|---|---|
| 4/12 | 1.054 | 25.3 ft. |
| 6/12 | 1.118 | 26.8 ft. |
| 8/12 | 1.202 | 28.8 ft. |
| 10/12 | 1.302 | 31.2 ft. |
| 12/12 | 1.414 | 33.9 ft. |
Trees
Wrapping a tree is like wrapping a cone. Its outside surface is π × r × √(r² + h²), where r is half the width and h is the height. Divide that surface by the wrap spacing (in feet) and you have the length of lights needed; divide by the strand length and round up for strands. Tighter spacing makes a brighter tree: 12 in. is a light wrap, 8 in. medium, 6 in. heavy.
Bushes
Most shrubs are rounded mounds, so the calculator lights the top (length × width) and the visible sides ((length + width) × height), then divides by the drape spacing. Netting or a zigzag drape both follow the same math.
LED vs incandescent wattage
An LED C9 bulb draws roughly 0.5 to 1 watt; an incandescent C9 draws about 7 watts. LED mini strands likewise use a small fraction of the power of the incandescent strands they replace. The practical result: a full roofline and several trees can often share one outdoor circuit, where incandescent sets needed several. Before connecting strands end to end, check the maximum number of connected sets printed on the strand or its box.
Where the prices come from
Every line in the shopping list is priced from Christmas Light Supplier: C9 LED bulbs in 25-packs or 500-bulb cases, 1,000 ft. socket wire spools, All in One clips, male plugs and female plugs, 4 in. and 6 in. LED mini strands, and photocell timers. Choose Installation kits for the roofline to price C9 kits instead of separate parts. Orders ship free, ship the same day, and have no minimum and no fees.
Frequently asked questions
How many Christmas lights do I need for my house?
Measure each roof edge you want to light and add them up. For C9 bulbs, the count is feet × 12 ÷ socket spacing: 100 ft. of roofline takes 100 bulbs at 12 in. spacing or 80 bulbs at 15 in. The calculator does this for every edge and adds the socket wire, clips and plugs.
How do I measure a gable without climbing the roof?
Measure the width of the gable at its base from the ground and pick the roof pitch (rise per 12 in. of run). Each sloped side is half the width times the pitch factor, and a gable has two. A 24 ft. wide gable on a 6/12 roof has two rakes of about 13.4 ft. each, 26.8 ft. total.
How many mini light strands for a tree?
It depends on the tree's size and how tightly you wrap it. The calculator treats the tree as a cone and divides its surface by the wrap spacing. A 7 ft. tall, 4 ft. wide tree wrapped every 8 in. takes about 69 ft. of lights, or three 25 ft. strands.
How many strands for a bush or shrub?
Enter the bush's length, width and height. The calculator covers the top (length × width) plus the rounded sides ((length + width) × height), then divides by the spacing between passes. A 4 ft. × 3 ft. bush that is 3 ft. tall, draped every 8 in., takes about 50 ft. of lights, two 25 ft. strands.
Should I use 4 in. or 6 in. spacing mini lights?
4 in. spacing minis pack more bulbs into each foot and give a denser, brighter wrap on trees and trunks. 6 in. spacing minis spread the same strand farther and suit larger shrubs and loose drapes. Pick one type per project so the brightness matches.
What does the shopping list include?
For the roofline: C9 LED bulbs, socket wire (or installation kits if you choose kits), a clip for every bulb, and a male and female plug for each edge. For trees and bushes: mini light strands, bought singly or by the 24-strand case, whichever costs less. Add photocell timers if you want the lights on at dusk.