Roof Slope Ratios

The following table shows how the same common roof slopes can be expressed using rise in run ratios degrees and percentages.

Roof slope ratios.

A ratio of 1 1 62 is known as the golden ratio and therefore the vast majority of roof pitch in degrees charts you see will be working to this ratio at the very least. Slope ratio a roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a 4 in 12 slope. Often you express roof pitch as the ratio between the rise and the run in the form of x 12. This will give you the rise over run or pitch.

See below after the table for directions on how to convert any roof slope from one form to another. Historically roof pitch was designated in two other ways. For example if you measure 4 inches the pitch of your roof is 4 12. Commonly used roof pitches were given names such as greek.

If the rise is 6 inches for every 12 inches of run then the roof slope is 6 in 12 the slope can be expressed numerically as a ratio. Simply locate a roof rafter board place the end of the level against the bottom edge and measure from the 12 inch mark vertically to the bottom edge of the rafter. A ratio of the ridge height to the width of the building span and as a ratio of the rafter length to the width of the building. Last updated july 10 2020.

You can assess this in two ways either as the roof pitch angles which the rafters make with the horizontal or the proportion between the run and the rise of the roof.