Refreshing the siding on your garden shed or detached garage is one of the most effective ways to boost curb appeal and protect your structure from the elements. However, ordering siding by the “Square” (the industry term for 100 square feet) can be confusing for DIYers. Order too little, and you’re left with an unfinished wall; order too much, and you’ve wasted hundreds on bulky boxes you can’t easily return.
Use our Vinyl Siding Calculator to determine exactly how many squares of material you need. We account for wall area, triangular gables, and deductions for windows and doors, while automatically adding a 10% waste buffer for cuts.
Vinyl Siding Calculator
How to Use the Siding Calculator
- Total Perimeter: Measure the distance around the entire base of the building in feet.
- Wall Height: The distance from the bottom of the siding (the starter strip) to the eave.
- Gable Peaks: The number of triangular sections at the top of your end walls.
- Deductions: The combined square footage of all windows and doors where siding will not be installed.
Why We Built This: Pro-Level Estimating
The “Secret Sauce” of this tool is the conversion into real-world purchasing units. Most calculators stop at square footage.
Our tool tells you exactly how many boxes to buy (assuming a standard 2-square box) and provides an estimate for J-Channel trim. J-Channel is the most forgotten component of a siding job—it’s the trim that hides the cut edges around doors, windows, and the top of the wall.
Educational Guide: Understanding “Squares” and Waste
In the siding industry, a “Square” is 100 square feet. Vinyl siding is almost always sold in boxes that contain 2 squares (200 sq ft).
A 10% Waste Factor is non-negotiable. Siding must be cut to fit around corners, gables, and openings. If you are installing complex patterns like Dutch Lap or Shakes, you may even need a 15% waste factor. Always store your extra siding in a flat, dry place—accidental damage from a lawnmower or weed whacker is common, and having a few spare panels from the same color batch is a lifesaver.
Frequently Asked Questions
Q: How many square feet are in a box of vinyl siding?
A: Most standard boxes of vinyl siding cover 200 square feet, which is equivalent to 2 “squares.”
Q: Do I need to remove old siding before installing new vinyl?
A: While you can install vinyl over old wood siding if the surface is flat and rot-free, it is always best practice to remove old material to inspect for water damage and install a proper house wrap (moisture barrier).
Q: What is J-Channel used for?
A: J-Channel is a trim piece with a “J” shaped profile. It is used to receive the ends of siding panels at windows, doors, and where the wall meets the roofline, providing a clean, finished look.
