Roof Pitch Calculator (Roof Slope Calculator)

The roof pitch calculator is a convenient online tool you can use to quickly assess the pitch of your roof to determine the length of rafters you need. After finding out your roof pitch angles, you can use the calculator to perform the calculations for you instead of doing them manually.

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How to use the roof pitch calculator?

This roof pitch calculator or roof slope calculator is a simple, easy to understand tool to use when you need to perform construction work in your home. To use this, you must take the required measurements so you can input them in the required fields. Here are the steps to follow for the roof angle calculator:

  • First, enter the value of the Rise and choose the unit of measurement from the drop-down menu.
  • Then enter the value of the Run and choose the unit of measurement from the drop-down menu.
  • Finally, enter the value of the Rafter Length and choose the unit of measurement from the drop-down menu.
  • After entering all of the values, the roof pitch calculator automatically gives you the values of the Roof Pitch, Roof Pitch (%), and Roof Pitch (x:12).

How do you calculate a roof pitch?

Roof pitch refers to the slope which the rafter creates. 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. Often, you express roof pitch as the ratio between the rise and the run in the form of x:12.

You can divide roofs into these categories:

  • Flat roofs which aren’t perfectly flat require a small slope to allow for water runoff. Generally, such roofs have a pitch ranging from 1/2:12 to 2:12.
  • Low-pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. These roofs have a pitch less than 4:12.
  • Conventional roofs are the easiest to construct and you can walk on them safely. They have a pitch ranging from 4:12 to 9:12.
    • High-pitched roofs often need extra fasteners and their pitch can be as high as 21:12.

You can also calculate roof pitch even without using a roof slope calculator. Use the following formula which also describes a right triangle. Here are the equations you may use to solve for the length of the slope and the rafter:

rafter² = rise² + run² (this formula is from the Pythagorean theorem)
rise / run = pitch, (use this when you express the pitch in percent)
pitch = tan (angle), (use this when you express the angle of the roof pitch in degrees)

What is the standard pitch of a roof?

Roof pitch refers to the measurement of the slope of a roof and you express this as a ratio. Although there’s isn’t any standard pitch of a roof used on all kinds of sloped roofs, you can determine the range of pitches by using a roof angle calculator and by considering factors like the local climate and roofing materials.

Express roof pitch as the ratio of the amount of the vertical rise of a roof or “rise” over the corresponding horizontal distance or “run.” You write the pitch assuming a run of 12-inches thus, the ratio would describe how much a roof rises for each foot of the run.

As aforementioned, there is no standard pitch of a roof. But the most commonly used pitches range between 4/12 and 9/12.

How do you calculate the slope of a roof?

When referring to roofs, the term “pitch” means two things. Most of the time, people use this term to refer to the roof’s steepness. But for carpenters and handymen, they believe that the term’s more accurate meaning is the overall dimensions of the roof. Either way, let’s see how you can calculate the slope of a roof without using a roof slope calculator:

1. Measuring the slope from the rafters

  • The most precise way to find the roof’s slope is by measuring it from the underside. Access one of the rafters then take the measurement this way.
  • Use a level against the underside of the rafter you’re measuring to get the most accurate value.
  • Locate the level’s 12-inch mark. If it doesn’t have this mark, use a tape measure to locate the mark and draw a mark on it.
  • Take the measurement of the vertical distance from the rafter to the level.
  • Write the slope down using the measurements you’ve taken.

2. Measuring the slope from the surface of the roof

  • Before taking any measurements, you must first confirm that it’s safe to walk on your roof. Check the surface of the roof and see if there is any structural damage. If you plan to take measurements on your roof, the best time to do this is in the morning when the sun is out so you don’t have to deal with the elements while you’re up there.
  • Take a measurement of 12-inches using a level.
  • Position your level against the roof until the bubble of the vial sits between two lines.
  • Take the measurement of the vertical distance from the level to the roof. Take note of this measurement and write down the value on a piece of paper.
  • Solve for the slope and write it down as a ratio.

What is the minimum slope of a roof?

The minimum slope of a roof depends on the roof’s profile. You need to consider the slope requirements of each panel to determine this minimum slope. The profile is the shape taken by the sheets when you bend them to form panels. Express the slope of a metal roof by a ratio which indicates the pitch of the roof.

This notes the rise of the roof for every foot of the horizontal run. In other words, you divide the vertical rise by the horizontal run. If you’re unsure, you may want to consult with the manufacturer of the panels with the values you’ve acquired from the roof pitch calculator before purchasing your materials.