How To Estimate Vinyl Siding

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Figuring out the right amount of siding is actually very easy.

A few things to know


Vinyl siding comes in 12-foot lengths.

All accessories also come in 12-foot lengths
Siding is sold by a “builder square”. Which are 100 square feet.

Two squares per box, for most types.

example: 10 feet by 10 feet.

So a whole box of siding is two squares or 200 square feet.

How Much Siding For a Gable End? How to figure siding for gable end of home?

Total height X total width = ??? Divided by 2 = ?? simple right.

Gable end siding

Let’s say you have a Bi-level house and it’s 50 feet long. Without measuring, the 50 feet part is easy, but measuring the height is a little bit more involved. You need to know that you have eight-foot floor ceilings, right? Let’s do this: you have the floor joist for the first floor, the floor joist for the second floor, and each one is about 12 inches x 2 plus your two levels (walls) @ 8 feet (96 inches)

2 floors (joist) = 2 feet

2 walls (levels) = 8 feet for a total height of 18 feet high.

So your house is 50 feet long by 18 feet high. Multiply those two numbers and you get 900 square feet.

Now you’re thinking, “but I have windows and a big sliding door…” And you’re right, but remember, the one thing you want to make sure of is that you have enough and you don’t want to start using little pieces towards the end of the job.

This is how I order. I get the total square footage and see what that comes to. Each box of siding comes with two squares in a box so you’re dealing with even numbers. If we have a total of 900 square feet, then you order ten squares. Which will be 1000 square feet and five boxes? Not 9 1/2. Remember, that 1/2 box is more likely to get damaged on delivery and hanging around until you use it, so it’s not worth not getting it. Once you’re done, you can always return full pieces using that long empty box that you now have.

On the other hand, let’s say you have a total of 825 square feet that you need. And you have some windows, and a door or two. Then I would order 800 square feet (four boxes).

J channel. This is the trim that goes around the windows and doors. I like to order two pieces per window and three per door no matter how small or big.

In this example, I only showed you one wall. Chances are, you will be doing more than just one side of your house. Just use the same vinyl siding formula on the other walls.

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  1. We are helping our grandson put vinyl siding on a 12 x12 shed, that is 7 feet high. The front has doors that are pretty wide, so maybe four feet on each side of the doors would need siding. Could you tell me what supplies would be required. Thx

    • Well if you want to seal it better use a house wrap, but for a shed, maybe not.

      Other than that you’ll need starter strips, J channels to go around the doors and windows if any. And siding of course.

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Written by Dominick Amorosso

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