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Estimating Your Siding Costs by Calculating
Your Exterior Square Footage

Detailed Method for Calculating Your Exterior Square Footage

by Robert Bury   Equations  |  Directions  |  Example

This information sheet is for estimating your siding costs. Soffits, fascia, custom work & additional accessories are extra. Not to worry though, most people just have their siding done and it’s typically the majority of your siding cost.  If you elect to have your overhangs covered, that is something that varies significantly due to the complexity of the install and what each company charges. When you request a free siding estimate with us you can also select a soffit estimate also.  Then you will have exact numbers so you can make an educated decision.


H x L = area of a rectangle
also see our
Square Footage Calculator


The rectangle formula will
work with any variation
of a rectangle.


(H x L) ÷ 2 = area of a triangle
Square Footage Calculator
for Triangles


the triangle formula will
work with any variation
of a triangle.


Tools needed: tape measure, calculator, paper & pencil

Special considerations: You are just trying to get an idea of how much your siding will cost. So, you don’t have to be exact with your measurements. By all means measure in Feet and round your measurements.

Example: 21 feet 8 inches could be 21 feet or 21.5 feet Keep it simple.

Siding prices are: for the purpose of this “How To Estimate Your Siding Costs” we are using a Top grade vinyl siding price of $4.50 per sq. ft.* Please refer to our prices page for other materials and options.

1) Pick a side of your home and draw the walls that will receive siding, breaking it into rectangles and triangles.

2) Now measure those rectangles and triangles. Write the measurements down on your drawing.

3) Continue around your house repeating steps 1 & 2, until you’ve measured your entire house.

4) Now add up all the rectangles and triangles. Use the formulas at the top of the page to get your areas for all of your rectangles and triangles. Add them all together. Now you have your house’s exterior square footage. (Fig. 4)

5) Last step, multiply the figure you came up with in step #4 times the siding cost per square foot. Example: $4.50 * 2300 = $10,350.00 Now you may add tax if it applies. Voila your done.

Example below.

Notes: The price you came up with is a “ball park estimate,” every house is different. I would have to write a book to include all possible variables and I want to keep this simple. So, please keep in mind your actual siding bid could vary

Here's an Example


This is a rough estimate of this examples top quality vinyl siding cost. The actual cost could vary slightly. Soffits, fascia, custom work, and custom accessories are extra. Please refer to prices page to see exactly what is included at the various siding packages per square foot bid.

Simple Method for Calculating Your Exterior Square Footage

1 to 1* Interior SqFt-equals-Exterior SqFt*

Keep in mind that this method is the least accurate but, it’s a quick way to get a “ball-park” idea of your exterior square footage.  Some houses are more and some are less but, for most houses this method works well.  This method has a variance of +/- 200 square feet in most cases and in rare cases +/- 500+ square feet.
* Please only use this method as a very general “idea” of your exterior square footage, never base any financial decisions off of this method.

  1. Get your homes interior square footage (livable space.)
  2. Add any other attached square footage (i.e.-an attached garage or unfinished room.)
  3. You now have your homes “ball-park” exterior square footage.*

This page is part of our 7 step Save On Siding™ system:

  1. Define Your Project
  2. Define What You Want (getting specific)
  3. How to Measure Your Home’s Exterior (and why you need this)
  4. SOS EDU 101 (inside info. & edu.)
  5. Get FREE Estimates (learning how & why)
  6. SOS EDU 201 (research & evaluation)
  7. How to Pick the BEST Estimate, Price & Company
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