- Measure only the edges people will see – usually the front and the sides facing the street.
- Eaves are easy: measure along the wall at ground level. Gables need a pitch multiplier.
- Bulbs needed = feet × 12 ÷ spacing in inches. Add about 10% for runs to the outlet.
- Installers price by the foot, so this number is also the key to comparing quotes.
Step 1: decide what gets lit
Walk to the street and look. Most displays light the front roofline, any gables facing the road, and sometimes the sides. Sketch the front of the house and mark each edge you want lit – that sketch is also what an installer will quote from.
Step 2: measure the eaves from the ground
The eaves run parallel to the ground, so you can measure along the wall underneath them with a tape measure or a measuring wheel, then add the overhang at each end (usually a foot or two). No ladder needed.
Step 3: measure gables with a pitch multiplier
Sloped edges are longer than they look. Measure the width of the gable at the bottom, halve it, and multiply by the factor for your roof pitch (rise in inches per 12 inches of run). Do that for both sides of the peak.
| Roof pitch | Multiply half the width by |
|---|---|
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 10/12 | 1.302 |
| 12/12 | 1.414 |
The multiplier is √(1 + (pitch ÷ 12)²) – plain geometry. If you do not know your pitch, 6/12 is a common middle value.
A worked example
A single-story home with a 50-foot front eave and one front-facing gable 30 feet wide at a 6/12 pitch:
- Eave: 50 ft
- Gable: half the width is 15 ft × 1.118 = 16.8 ft per side, so 33.5 ft for both sides
- Total: about 84 feet of roofline
Step 4: turn feet into bulbs
Bulbs = feet × 12 ÷ spacing in inches. At 12-inch spacing that is one bulb per foot; at 15 inches about four bulbs for every five feet. For the 84-foot example, that is about 84 bulbs at 12 inches or 67 at 15 inches. Add around 10% of wire for the run down to the outlet and any gaps.
Step 5: use it
- For quotes: installers price by the foot – $2 to $5 according to Angi, $5 to $12 according to HomeGuide. See the cost guide.
- For power: the bulb count tells you how many circuits you need – see how much it costs to run Christmas lights.
- For a quick estimate: the roofline estimator on our homepage gives typical footage for one, two and three story homes.
Keep reading
- C7 vs C9 bulbs
- Hanging lights without damaging your roof
- How much it costs to run Christmas lights
- Christmas light installation cost
Sources
- Angi – How much does Christmas light installation cost? – updated May 3, 2026; read September 22, 2026
- HomeGuide – Christmas light installation cost – updated October 1, 2025; read September 22, 2026
Written by the Christmas Lights Outdoor Installation editorial team. Figures are dated and linked to their source; national numbers vary by area – confirm with local installers.
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