- Siding Squares:Siding is always sold and quoted in "squares." One square equals exactly 100 square feet of surface coverage.
- Deductions: You do not need siding over your windows and doors. Measure them and subtract their area from your gross wall area. An average window is 15 sq ft; an average door is 21 sq ft.
- Trim Components:Don't forget the accessories! You need Starter Strips for the bottom row, J-Channel to go around windows/doors, Corner Posts for the outside/inside corners, and Utility Trim for under the eaves.
The Complete Guide to Measuring for Vinyl Siding
Upgrading your home's exterior with vinyl siding is a major project, but estimating the materials doesn't have to be intimidating. By breaking your home down into simple geometric shapes, you can accurately determine exactly how much siding you need to order.
Our Vinyl Siding Estimatordoes the heavy lifting for you. It takes your gross measurements, subtracts the space taken up by doors and windows, applies a professional waste factor, and tells you exactly how many boxes or "squares" to buy.
How to Measure Your House for Siding
Grab a tape measure and a notepad, and head outside. You need to calculate the area of two distinct shapes on your house:
- Rectangular Walls: Measure the width of the wall from corner to corner. Measure the height from the foundation line up to the eaves (where the roof overhangs). Multiply Width x Height to get the square footage. Do this for all four sides of the house.
- Gables (Triangles): The gable is the triangular section of wall just under the peak of a sloped roof. Measure the width of the base of the triangle. Then measure the height straight up from the center of the base to the roof peak. Multiply the Base x Height, and then divide by 2. Add this to your wall total.
Accounting for Windows and Doors
Once you have your total (gross) square footage, you need to subtract the "holes" in the walls. Count all your windows and doors. You can measure each one individually, or use standard averages: 15 sq ft per window, and 21 sq ft per door. Subtract this total from your gross wall area to find your Net Siding Area.
Why You Must Calculate a Waste Factor
You can never buy just the net area. Siding is installed in long, horizontal panels. When a panel hits a corner or a window, it must be cut. The leftover piece is often too short to use elsewhere and goes in the trash.
Always multiply your net area by a waste factor before dividing by 100 to find your squares. A standard rectangular home requires 10% waste. If your home has multiple stories, bay windows, and several gables, increase the waste factor to 15%.
Frequently Asked Questions
How do I calculate how much siding I need?▼
Measure the width and height of each exterior wall and multiply them to get the total square footage. Do this for all walls, including gables. Then, subtract the area of all your windows and doors. Finally, divide the total net square footage by 100 to determine how many 'squares' of siding you need to buy.
What is a square of siding?▼
In exterior construction, a 'square' is a unit of measurement equal to exactly 100 square feet. Because siding covers large areas, manufacturers package and sell siding in boxes or bundles that add up to either 1 or 2 squares.
How much extra siding should I buy for waste?▼
You should always add a waste factor of 10% to your total net square footage. Siding must be cut to fit around corners, windows, and roof lines, and the offcuts are often unusable. For complex homes with many gables and dormers, add 15%.
What is J-Channel?▼
J-Channel is a trim piece shaped like the letter 'J' that is installed around windows, doors, and where the siding meets the roof (soffit). It provides a finished channel for the siding panels to slide into, hiding the cut edges.