Calculating Roof Pitch for Dummies

Inputs to pitch calculation

In our wanderings around the internet, the research team here at the Antisocial Network continue to be just flabbergasted at some of the inane crap that money-grubbing freelancers have published; not that it's been published, of course, but that these people actually got paid for doing such a lousy job of it. Today's awardee is a case in point: the author of well over a hundred eHow.com posts across a wide range of categories, Carter McBride, JD, has already gotten the nod once before for overthinking a simple mathematical operation. He's back today, holding forth on another topic about which he clearly knows nothing: "How to Calculate Pitch."¹

As is so often the case with eHow.com contributions, this freelancer tips off his or her readers that the content is bullshit in the introduction. McBride's post is no exception:

"Pitch is an important concept for building your roof. The pitch is how steep your roof is... The basic formula for pitch is rise over run. The rise is the height of the roof. The run is the half the size of the house..."

Umm, yeah: Carter's right that pitch is important and sort of gets the concepts of rise and run right. Where he went wrong is simple: he apparently did not know the units of pitch.  The pitch of roofs is typically stated as inches of rise per 12 inches of run, e.g., 3/12 or 5/12. And "half the size of the house"? that's a pretty ambiguous phrase, wouldn't you say, folks?

Required by DMS to provide an example of his calculations, McBride describes his hypothetical building: "Measure from one end of the house to the other end of the house, then divide by two to calculate your run. For example, imagine the house measures 20 feet, so the run is 10 feet.  Measure from the steepest point of the roof downward to where the roof starts. This is your rise. In the example, assume the rise is five feet."

Not particularly... good descriptions: "from one end of the house to the other"? and "from the steepest point of the roof"? Both descriptions are utter bull: apparently he means the horizontal and vertical distances from roof edge to roof peak (just in case you didn't know, Carter, there is such a thing as a "shed roof"). Of course, it only gets worse from here. McBride then instructs his readers to

"Divide the rise by the run. In the example, five feet divided by 10 feet equals a pitch of 0.5."

Well, no, Carter, the slope of that roof is 0.5. Its pitch, on the other hand, when stated in units a builder (or a rafter calculator) can understand, is 6 / 12 -- a rather steep roof, we think.

McBride could have asked someone who knows what he or she is talking about and even verified his post by visiting a roof pitch calculator. He did not, however, instead choosing to join dumbasses like Lacy Enderson and Mark Fitzpatrick in spreading misinformation. You know that that makes Carter, right? It makes him our Dumbass of the Day

¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was    ehow.com/how_8538466_calculate-pitch.html

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