Installing vinyl sidings is a laborious and time-consuming job. It will not only exhaust you physically, but mentally as well as you will need to do some math along the way.

Estimating how much siding you need to completely cover the exterior of your house, for instance, requires taking precise measurements. To accurately estimate the number of panels that you will need, you must also consider factors like the numbers of windows and doors that your home has — thus the math requirement. 

On the brighter side, this does not mean you cannot do the project! You just need to be attentive and patient while learning how to accurately measure and calculate. 

How to Estimate the Amount of Siding You Need

Finding out the number of squares of siding you will need is actually quite simple. It all depends on the size of a house’s wall and gable. This estimate is also easy because repairmen have come up with a formula for each area to calculate the exact number of squares you will need. 

Does this sound complicated?

It is a little, but before we proceed to the estimation part, let’s talk about a few factors that you should consider while taking measurements.

Things You Must Consider

1. The number of windows and doors. Naturally, a wall (or a gable) with windows and doors will need less siding compared to those without. To take them out from the total size, measure width and height of the door(s) and/or the window(s). 

Once you have the measurements, simply multiply the width and height. After that, subtract it from the total square footage of the gable or wall.


 2 feet wide x 4 feet tall window = 8 feet

 21 feet (gable’s size) – 8 feet = 13 feet

2. The type of trim you will use. Aside from its aesthetic purpose, trim is a material used to enclose doors and windows with siding. And these materials occupy a small amount of space.

There are four kinds of siding trims: the J-channel, Starter Strips, Undersill, and Corner trim. Each trim varies in size and although they all have the same purpose, each has a distinct function. 

Here’s how they differ:

  • Starter strips. The starter strips are typically used in the bottom part of the wall. Essentially, they help keep the bottom part of the siding sturdy. 
  • J-channel trim. J-channel is often placed on the top part of the wall. It serves as a cover for siding with exposed edges and is often used to protect the edges of doors and windows.

    Professional repairmen also use this type of trim for the inner corner between two pieces of siding. 
  • Undersill trim. Also known as a utility trim, the undersill trim is used to cover the top edge of the siding. It is usually placed above the wall and the soffit.
  • Corner trim. As its name suggests, the corner trim is placed on the outside and inside corner between two planks of siding. Primarily, it is used to cover the outer edge of the siding.

3. Order additional materials. While the purpose of measuring and calculating the amount of siding needed is to save money, ordering additional pieces of siding can be a good idea.

Trims, cutoffs, and mistakes during installation are unavoidable, especially for inexperienced folks. And it would be a bit inconvenient to order materials again and again. So, make sure to order extra squares. Professionals recommend an additional 10%. 

Wall and Gable Measurement

Now that you have an idea of what factors you must consider when taking your measurements, let’s proceed to the measuring process. 

How to Measure the Wall

To estimate how many squares you will need for a wall, simply measure its width and height. After that, multiply the two to get the total square footage of the wall. Lastly, divide the wall’s size by 100.


50 feet wide x 15 feet tall wall = 750

750 / 100 = 7.5

Note: A square of vinyl siding can cover 100square feet. Hence, the total square footage being divided by 100. 

How to Measure the Gable Walls

For the gable wall, the method is almost the same as the standard wall. You need to measure the height and width of the gable, then multiply the two to get the total square footage of the gable. 

Once done, divide the gable’s size by two, then divide that answer by 100. 


30 feet wide x 20 feet tall gable = 600

600 / 2 = 300

300 / 100 = 3

Are There Siding Measurement Tools?

If the mentioned formulas are quite taxing for you, opt for an AI-powered calculator instead. This job requires accurate measurements and calculations and many contractors, as well as DIY enthusiasts, fail to do the job precisely. 

This is why siding measurement apps have been developed. 

That said, here are a few apps you can use:

  • Contractor calculator. The Contractor Calculator is a type of application that can help you estimate the amount of siding you need by simply putting the measurements of your home (and the measurements of its doors and windows) into the app. It is best for folks who do not like math or memorizing formulas. 

    There are other apps with the same function too. 
  • James Hardie contractors eye app. While the Contractor Calculator does half of the process, the James Hardie Contractors Eye app will do all the work for you. With 95% accuracy, the Contractors Eye app can tell the measurements of siding, doors, windows, and trim by simply taking pictures of a house’s exterior.

    Hence, you do not need to manually measure your wall and gable as well as the door and windows. 
  • Hover. While similar to the Contractors Eye app, the Hover app allows contractors to estimate the amount of siding needed remotely. Essentially, it lets owners upload pictures of their homes so contractors can have them checked immediately. 

Should You DIY or Hire Professional Installers?

Calculating how much siding you need for your siding installation project can help you a lot, particularly in terms of labor and material cost. As such, the answer to whether you should hire a team of professional installers or do it yourself depends heavily on your skill and experience.

If you are not confident in your skill, though, then you might as well hire someone else to do the work. 

Editorial Contributors
Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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