Step by Step Measuring for a New Roof – Tools Needed and Calculations for Area


Taking the measurement of the roof is very important work before buying materials for re-roofing. You can save significant money and time by estimating the cost of required for roof replacement. You don’t need to be a professional; however, you only need some patience and some geometrical knowledge. Furthermore, you will require a ladder, pencil, paper, measuring tape, carpenter’s level, measuring wheel, and calculator for completing this job.

The simple way of measuring your roof is described below.

Make a Rough Drawing

The rough drawing of the roof is very useful to remember all the measurements accurately. It reduces the chances of any confusion.

  • The first step of this part is to make a rough sketch of the roof.
  • Show every part of your roof on the sketch such as rake, valley, hip, and ridge.
  • You should draw pipes, vents, chimneys, skylights and solar panel also, if there.

Try to draw it in some proportion; however, it’s okay if the sketch is not perfectly scaled.

Measurering a roof

Measuring the Slope

If you measure the slope first then you will save significant time. You will need an inclinometer to measure the inclination or angles of inclined parts of the roof. It is a very useful and cheap instrument to measure inclination of any object, and uses gravity to measure the slope. It is also known as a tilt meter, slope gauge, slope indicator, or gradient meter.



Image: Pinball Magic

Roofs are of all different shapes. Due to this, the measurement of slopes of all inclined parts of the roof is required during the calculation of area of the roof. Actually, we have to divide the entire roof into different shapes such as triangles, squares, and rectangles in order to simplify the calculation of area. The calculation of slopes helps us to calculate the area of different shapes.

Taking the Measurements

The most famous tool for the measurement of different parts of the roof is the measuring wheel. This tool makes your work easier because it is fast and it doesn’t need another person to hold the other side of the tape. However, it is a mechanical device; due to this, it’s very important to check it whether it is working properly or not.

Besides, if you don’t feel comfortable with this device, you should go for flat measurement using measuring tape. However, it takes much more time than measuring wheel for measuring all parts of the roof. Furthermore, we get less precise measurement by measuring tape.

Now, record the vertical, horizontal and diagonal measurement of the roof on your sketch. This will help you to estimate the required quantity of roofing material.

Calculating the Area

Now, it’s time to use the measurement, taken by you to, calculate the area of the roof.

  • First, you will need to divide the roof into rectangular and triangular sections.
  • It doesn’t matter how complex the roof is. You can make series of sections of the roof in terms of square, rectangle, and triangle.
  • When you will make sections, then only simple mathematics is required to apply. Because, calculating the areas of such sections are very easy.
  • If you number these sections, it will be very helpful and easy to remember.
  • When you calculate the area of each section, add all areas to get the whole area of the roof.

Figures regarding the calculation of triangle and rectangle are given below.

Example of using the slope during measurement of area

If your roof is steeply pitched, you don’t need to climb up on the roof to get your measurement. You only need to use the inclinometer and measurement the slope of the roof. This is the advantage of calculating the slope. If you are confused about the use and requirement of calculation of slope then here is a description of how the calculation of slope is useful.

The image below and the calculation of the area of the roof on the image will give you an idea about the use of the slope.

Pitched roof

Calculation of the area of the part ‘abcd’

  • Go to the front, i.e., second image.
  • Measure the distance ‘bf’. (You can get help of any another person for this.)
  • Measure the inclination of the roof. Let the measurement of the slope be x°.
  • Divide the bf by 2. You will get the distance ‘be’
  • Calculate the distance ‘ab’. It’s an trigonometrically calculation, and the step of the calculation is

Cos x = bf/ ab

  • After getting the value of ab, measure the distance ‘bd’ using measuring tape.

Now the final area of the one part of the roof, i.e.,

‘abcd’ = ab * bd

And the area of the whole roof will be = 2 * abcd

Calculation of divided shapes

Area of Triangle using angle between two sides (we can measure the angle using the inclinometer)

Area of triangle

Area of Rectangle

Area of Rectangle

Calculate Shingles Required for the Roof

roof shingles

The calculated areas will help you to estimate the material required, but, to calculate required shingles for your starter course, just add linear feet at the eave and divide the result by the length of one shingle. This will make an estimate of required shingles. Shingles are available in different shapes; therefore, you have to make sure, which type of shingles you want to use before the calculation. Here are some points regarding shapes of shingles.

  • You have two choices for shingles; use pre-cut shingles or three-tab shingles. Both are fine; you can use any of them. However, they don’t have the same coverage. Three-tab shingles cover approximately 33 linear feet of hip or ridge, and pre-cut shingle’s covers comparatively more space.
  • Keep in mind, some shingle packages offer 3 bundles per square, and some packages offer 4 or more bundles per square. Use of fewer bundles is better.
  • Buy extra shingles for any shortage, but keep them in a suitable place so that they can be returned if not used.
  • In the US, shingles are usually sold in 100 sq. ft. bundles; therefore, if you are using shingles of this shape then you will need to divide the whole area of the roof by 100, and you will get number of shingles required for the roof.


The entire process involves four parts- measurement of slope, measurement of roof, area calculation, and the final work is to calculate required shingles- to replace the roof. Try to make all measurements with patience in order to get the most precise calculation of required shingles and other materials.


Image- Measurering a

Image- Roof