How to Measure Your Roof Pitch (and Order the Right Size Triangle Gable Vent)
Ordering a triangle (gable-end) vent isn't just about width and height: it also has to match your roof's slope, or pitch. Get the pitch wrong and even a perfectly built vent won't sit flush against your siding. Here's how to find your roof pitch in a few minutes, and how that pitch determines the exact vent size you should order.
What Is Roof Pitch?
Roof pitch is the steepness of your roof, expressed as a ratio of rise to run: how many inches the roof rises vertically for every 12 inches it runs horizontally. A "6/12 pitch" roof rises 6 inches for every 12 inches of horizontal run. The higher the first number, the steeper the roof. Most homes fall somewhere between a 4/12 (fairly shallow) and a 12/12 (very steep, a 45-degree angle).
Your triangle gable vent needs to match that same ratio, because its two angled sides follow the same slope as your roofline. That's why "pitch" is one of the first things we ask for when you order a custom triangle vent.
How to Measure Your Roof Pitch
You don't need to climb on the roof. Either of these methods will get you an accurate pitch in a few minutes.
1. Use a Level and Tape Measure
All you need is a tape measure and a level. Go into your attic where you can see a rafter clearly. Starting at any point on that rafter, use the level to measure 12 inches from it and hold your tape measure straight up and down. Use the level to make sure it's not leaning. Whatever that straight-up measurement is, in inches, is your rise. For example, if it's 6 inches, you have a 6/12 pitch.
2. Match Your Existing Gable Trim
If you're replacing an existing vent, its old opening already carries your roof pitch. Hold a rafter square against one of its angled edges, or take a photo straight-on with a level or square in frame, and match the angle against the square's scale. Prefer not to measure the roof itself? Try our free roof pitch calculator, which figures out your pitch from your existing vent's width and height.
How Pitch Determines Your Triangle Gable Vent Size
A triangle gable vent is a symmetrical triangle centered under your roof peak, so its height is locked to its width by the same rise-over-run ratio as your roof. Once you know your pitch and the width you need, the formula is:
Vent Height = (Width ÷ 2) × (Pitch Rise ÷ 12)
Pitch-to-Height Reference Chart
Here's what a 48"-wide triangle vent works out to at each common pitch, using the formula above. Your exact width options vary by pitch. Check the product page for the full range available at your pitch.
Roof Pitch | Rise per 12" Run | Height at 48" Width |
4/12 | 4" | 8" |
5/12 | 5" | 10" |
6/12 | 6" | 12" |
7/12 | 7" | 14" |
8/12 | 8" | 16" |
9/12 | 9" | 18" |
10/12 | 10" | 20" |
11/12 | 11" | 22" |
12/12 | 12" | 24" |
Choose Your Material and Trim Style
Once you know your pitch, pick a material and trim style below and you'll land on the product page for that combination, where you can select your exact width and see the matching height.
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