**How to Measure a Quonset Roof**

- Measure the horizontal width of the Quonset roof to determine the diameter. …
- Multiply the diameter dimension time 3.14, referred to as “pi,” and then divide the result by 2 to determine the circumference measurement of the Quonset roof.

# How to Measure the Roof of a Round Building

1 . Measure the outer diameter of the building.

2 . Measure the amount of horizontal overhang between the building’s outer wall and the roof’s outer edge.

3 . Multiply the amount of overhang by two to include the opposite side of the building.

4 . Add the total overhang to the diameter. For example, a building diameter of 20 feet and an overhang of 1 foot on one side results in a total roof diameter of 22 feet.

5 . Measure the length of the rafters from the peak to the lower edge.

6. Calculate the total surface area of the roof using the following formula: pi times the radius times the rafter length, also called the slant height. To find the surface area using the diameter in the previous example and a rafter length of 20 feet, use the following calculations and use 3.14 as an approximation for pi:

Radius = 22 / 2 = 11.

Surface area in square feet = 3.14 * 11 * 20 = 690.8.

7 . Determine the vertical height of the roof by finding the square root of the result of subtracting the squares of the rafter length and the radius. Using the previous results, the answer would look like this:

Rafter length squared = 20 * 20 = 400.

Radius squared = 11 * 11 = 121.

So 400 – 121 = 279.

The square root of 279 is approximately 16.7. In this example, the vertical rise of the roof is 16.7 feet from the outer edge to the peak of the roof.

# Measuring Roof Slope and Pitch

**Slope**

**Slope Ratio**

The slope can be expressed numerically as a ratio. The slope ratio represents a certain amount of vertical rise for every 12 inches of horizontal run. For example, a “4 in 12” slope can be expressed as the ratio of 4:12. A “6 in 12” slope is expressed as 6:12.