Roofline lighting calculator

How many feet of lights do you need? Enter your eaves, gables and porch to estimate the run for permanent or seasonal lights.

The result estimates coverage. Check kit length and extension compatibility before ordering.

Your roofline

Front eave, straight run

Gables facing the street

Width of each gable

Roof pitch

Porch roofs, garage returns, anything else you want lit

Not sure about the eave length?

Pace it out. A normal adult stride is close enough to three feet, and being two feet over on a hundred-foot run changes nothing. The measuring guide has the careful version.

You need

119ft

Front eave: 72.0 ft
Gable rakes, both sides: 26.8 ft
Porch and returns: 14.0 ft
Waste allowance, 5%: 5.6 ft
Total: 118.4 ft

Buy this

One 150 ft run — cost tier High-end

Govee Permanent Outdoor Lights 2, 150 ft · 150 FT · 108 ZONES · 17 IN SPACING · IP67

A 100 ft kit would leave you 19 ft short, which usually means the porch goes dark. This one leaves 31 ft spare. Kits come in fixed lengths, they do not extend, and the joins are proprietary, so round up on the first order rather than planning to top it up later.

See the price at the retailer

Price tiers are our own rough budget bands, not live prices. Check the listing for today’s price.

Compare every kit that runs 119 ft

The arithmetic, if you want to check it.

The eave is a straight run, so you measure it and that is the number. The gable is the part people get wrong: the sloping rake is longer than the wall underneath it, and how much longer depends entirely on the pitch.

Take half the gable width, multiply by the factor for your pitch, then double it for the two sides. A twenty-four foot gable at a six-in-twelve pitch gives twelve feet, times 1.118, times two — 26.8 feet of rake.

Then add five per cent. You lose it at corners, at the gable peak, and to the run back down to the outlet. What you buy is that total rounded up to a whole foot, because nobody sells you a fraction.

rake = (width ÷ 2) × factor × 2 × gables

total = (eave + rake + extras) × 1.05

factor = √(1 + (rise ÷ 12)²)

Rafter factor by roof pitch, and the rake it gives on a twenty-four foot gable.
Pitch	Factor	24 ft gable
3 / 12	1.031	24.7 ft
4 / 12	1.054	25.3 ft
5 / 12	1.083	26.0 ft
6 / 12	1.118	26.8 ft
7 / 12	1.158	27.8 ft
8 / 12	1.202	28.8 ft
9 / 12	1.250	30.0 ft
10 / 12	1.302	31.2 ft
12 / 12	1.414	33.9 ft

Typical houses, worked out.

If your house is close to one of these, start there and adjust. Every figure includes the five per cent waste and is rounded up to a whole foot.

House	Frontage	Gables	Buy	Kit
1,200 sq ft ranch	40 ft	none	42 ft	100 ft kit
1,800 sq ft two-storey	44 ft	1 × 20 ft at 6/12	70 ft	100 ft kit
2,400 sq ft two-storey	56 ft	2 × 22 ft at 8/12	115 ft	150 ft kit
3,200 sq ft, wide front	70 ft	2 × 26 ft at 9/12	142 ft	150 ft kit

None of these rows carries a porch or a garage return. Add those in the box marked extras and the number moves, usually by ten to twenty feet.

What people get wrong.

Measuring the wall, not the rake

The sloping edge of a gable is between three and forty per cent longer than the wall below it. On a steep roof that is the difference between having enough and not.

Forgetting the run to the outlet

The controller has to reach power. That is often ten or fifteen feet of the run doing nothing decorative, and it comes out of the same hundred feet.

Buying exactly enough

You cannot buy nineteen more feet later. Kits come in fixed lengths and the joins are proprietary. Round up on the first order or live with a dark porch.

A number is not a picture.

119 feet tells you what to buy. It does not tell you whether you will like it. Every kit that covers this run is rendered on the same three houses, at the same dusk.

See them lit