A roofing square is used by roofers and contractors as a measuring unit for estimating and calculating roof size in a standardized manner, where every 1 roofing square = 100 sq. ft. This is more or less a universally applicable size for roofing squares, unless any deviation from the 100 sq. ft. per roofing square rule is specified for the particular project. Such deviations are not common at all though, except when dealing with very small structures.

Why Professionals Use Roofing Squares as a Measuring Unit

There are two primary reasons as to why the roofing square is a preferred unit for roofers and other construction professionals. The first would be convenience. A bigger unit makes it easier and faster to calculate how much material would be necessary to build, replace or repair roofs.

The second reason is standard applicability. A roofing square is universally applicable for measuring the quantity of materials that would be necessary to cover a 100 sq. ft. of roof, irrespective of the roof layout and shape.

Calculating and Converting Roof Measurements in Roofing Squares

In order to have a basic estimation of your roof size in roofing squares, first find out the total size of your roof in square feet, in case you are not aware of it already. Then simply divide this by 100 to convert your roof’s measurements into roofing squares. As you might have noticed, we have only used “estimation” rather than the term calculation. This is because what we have at this point is only a rough estimation of the roof’s size in roofing squares. In order for it to qualify as a proper calculation, two other aspects must also be taken into account, which are:

  1. The slope
  2. Plane size

Should You Try to Calculate the Roof Size on Your Own?

Unless you have sufficient experience to undertake such a task, it would be ill-advised to try and measure the roof on your own. It is best left to the professionals for the sake of both accuracy and safety. However, you can learn to do so with some expert guidance. If you are a beginner in DIY home renovations, here is a brief, introductory guide on how to get the roof measurements on your own.

Roof Measurements: The Planes

Climb your roof with a measuring tape, a notepad and a pencil. Do not forget to stabilize your ladder first, before stepping on it. Place the ladder in such a way that it doesn’t make it difficult for you to come down. It is a common beginner’s mistake to forget that you will also be climbing down the same ladder!

Once you are on the roof, use your measuring tape to measure the lengths and the widths of every plane. Do not forget to write down the measurements as soon as you take them. Note that features and additions such as porch coverings, skylights, dormer windows, and extended garages likely mean that there are multiple planes for you to measure, and not just two.

Roof Measurements: The Pitch

You will also need to have an accurate estimation of the pitch if you are to properly calculate your roof’s total area. Fortunately, you will not need to get on top of your roof for this one, as the pitch of your roof can easily be measured from the attic itself. You will be needing the same notepad, tape and pencil which you used to measure the planes, with only the addition of a 24-inch level to your arsenal. We will briefly introduce the steps necessary for measuring the pitch next:

  • Take and mark a measurement of 1 foot/12-inches from one end of the level
  • Place and hold the other end of the level firmly against the bottom of any roof rafter
  • Take a vertical measurement from the previously made 1-foot/12-inch mark until you reach the rafter’s bottom side
  • Note it down and you are done

The measurement which you will have on your notepad is the pitch, aka, how many inches your roof rises with every foot of elevation. You may need assistance in holding the level in place, as that can make for more accurate measurements. However, it is not that difficult to get done without help.

Getting the Final Roof Measurements

Manual conversions can take up a lot of time, but they are generally more accurate. However, the difference is mostly minimal or non-existent in most cases, so we advise saving time and using a roofing calculator to convert your measurements into a number that represents the final size of the roof. Nevertheless, if you are particularly keen on knowing how to do it on your own, apply the following steps:

  1. Divide the pitch by 12
  2. Multiply the result by itself, which is called squaring in mathematics
  3. Add 1 to the result
  4. Calculate the square root of the present number
  5. Multiply the roof’s length and width previously recorded to get the measurement in square feet
  6. Add the number you got from step 4 to the number you got from step 5 to get the estimated area of the roof in sq. ft.
  7. The rule for roofers is to add an extra 10-15% of the total roofing area you calculated if you are measuring a gable roof
  8. The extra area that must be added to the final number could need raising by as much as 17% if we are discussing a cottage roof

Now, all you need to do is divide the final number by 100 and the result would be instantly converted to roofing squares. Just in case you are wondering why the extra percentages were added to the final number, it is an essential allocation for hips and ridges. There will also be at least some amount of the material that will be lost as waste during the various mixing, cutting processing, etc. 

This should be all you need to know about measuring roofs and converting their measurements into roofing square units for standardized calculations.