Nobody wants to make two trips to Home Depot. This calculator tells you how much siding you actually need so you can buy it once, install it, and move on with your life.

Punch in your wall dimensions, tell it how many doors and windows you've got, and it spits out the number in "squares" — which is how siding is actually sold. Works for vinyl, Hardie board, wood, whatever. Works for houses, garages, sheds. Works for that one wall the previous owner inexplicably covered in asbestos shingles that you've been meaning to deal with for three years.

Let's get you a number.

Walk into a lumber yard and ask for "enough siding for 1,400 square feet" and watch them do math in their head. Ask for "14 squares" and they'll point you straight to the aisle.

One square = 100 square feet. That's it. The building industry just bundles things in hundreds to make ordering easier.

The other thing to know: vinyl siding usually comes in boxes that cover 2 squares each. So 14 squares = 7 boxes. Fiber cement is weirder — sold by the plank or bundle — so you'll need to check the coverage on your specific product.

Contractors quote by the square. Material is sold by the square. Once you think in squares, everything else makes sense.

Look, I'm not going to pretend this is fun. You're going to be outside with a tape measure, probably on a ladder at some point, hoping your neighbor doesn't ask what you're doing.

But it's not complicated. Here's the process:

1. Measure width. Ground level, corner to corner. Write it down.
2. Measure height. Foundation to roofline. Write it down.
3. Multiply.
4. Repeat until you've done every wall.

That's your total square footage. A 40-foot wide wall that's 12 feet tall is 480 square feet. Do that four times and add it up.

Gables are the triangular bits where your roof peaks. They throw people off because — surprise — triangles aren't rectangles.

The formula: Width × Height ÷ 2

That's it. A gable that's 30 feet wide and 8 feet to the peak is 120 square feet, not 240. The calculator handles this automatically when you select "Gable" mode, so you don't have to remember the formula. Just enter width and peak height.

Round up. If something measures 38 feet 9 inches, call it 39. Or 40. You're buying siding, not cutting diamonds.

Measure outside. Interior room dimensions don't account for wall thickness. Doesn't seem like much until you're short a foot on every single wall.

Draw a picture. Even a terrible one. Label each wall. Future you, standing in the siding aisle trying to remember if the garage wall was 22 or 28 feet, will be grateful.

The wall behind the deck still needs siding. So does the one blocked by the air conditioning unit. So does the one you can barely see behind those overgrown bushes you keep meaning to trim. Ask me how I know.

There's a dropdown. It matters.

Wall: Rectangle math. Width times height.

Gable: Triangle math. Width times height, divided by two.

The picture at the top changes when you switch modes — look at it. If your roofline cuts diagonally through the section you're measuring, that's a gable. If it's a flat wall with a straight top, that's a wall.

Most houses need both. Do separate calculations for each section and add them at the end.

Pick wall or gable. Look at the diagram if you're not sure.

Enter width and height. Feet only. For gables, "height" is from the top of the rectangular wall portion to the roof peak.

Count openings. Doors and windows. The calculator assumes standard sizes — roughly 20 sq ft per door, 15 per window. If you've got something unusual (a giant picture window, double doors, a wall that's basically all glass), you might need to adjust manually.

Read the result. Squares for ordering, square feet for double-checking the math.

Repeat. Do every wall and gable, then add them together.

A typical house might need 6-10 separate calculations. It goes faster than you'd think.

Straightforward single-story, nothing weird:

• Front/back walls: 50' × 10' = 500 sq ft each
• Side walls: 30' × 10' = 300 sq ft each
• Openings: 2 doors, 8 windows

Math:

• Total walls: 500 + 500 + 300 + 300 = 1,600 sq ft
• Minus doors (40) and windows (120) = 160 sq ft
• Net: 1,440 sq ft → 14.4 squares
• Plus 10% waste: ~16 squares

Order 16 squares / 8 boxes of vinyl. Done.

Getting more complicated:

• Main walls: 40' × 20' = 800 sq ft (×2)
• Side walls: 30' × 20' = 600 sq ft (×2)
• Two gable ends: 40' wide × 6' peak = 120 sq ft each (remember, triangles)
• Openings: 1 door, 14 windows (two stories = lots of windows)

Math:

• Walls: 2,800 sq ft
• Gables: 240 sq ft
• Total: 3,040 sq ft
• Minus openings (230 sq ft): 2,810 sq ft → 28.1 squares
• Plus 15% for complexity: ~32 squares

More windows means more cuts means more waste. Budget accordingly.

Your spouse wants it to match the house. You want it done by Saturday. Here's the siding math for a standard 10×12:

• Two walls: 12' × 8' = 96 sq ft each
• Two walls: 10' × 8' = 80 sq ft each
• Openings: 1 door, 2 tiny windows

Math:

• Total: 352 sq ft
• Minus openings (50 sq ft): 302 sq ft → 3 squares
• Plus 10%: ~3.3 squares

Buy 4 squares (2 boxes). Yes, you'll have nearly a full square left over. No, you cannot get away with buying just 3. I promise you will regret it.

Real houses aren't rectangles. Here's one with a bump-out — you know, that breakfast nook addition from 1987 that juts out 8 feet on one side:

Main house:

• Front: 45' × 18' = 810 sq ft
• Back: 45' × 18' = 810 sq ft
• Sides: 28' × 18' = 504 sq ft (×2)

That stupid bump-out:

• Three exposed walls, each 10' × 10' = 300 sq ft total

Two gables:

• 28' × 5' ÷ 2 = 70 sq ft each = 140 sq ft

Openings: 2 doors, 16 windows (previous owners loved natural light)

Math:

• Main: 2,628 sq ft
• Bump-out: 300 sq ft
• Gables: 140 sq ft
• Minus openings (280 sq ft): 2,788 sq ft → ~28 squares
• Plus 15%: 32 squares

Miss that bump-out and you're 3 squares short. This is why you walk around the entire house with a notepad.

Siding projects waste material. It's not a flaw in your planning; it's physics. Panels get cut to fit. The offcuts don't fit anywhere else. Somebody drops one. Somebody measures wrong.

Add extra.

Here's a story: Guy in my neighborhood was siding his detached garage. Did all the math right. Ordered exactly 8 squares. Got to the last wall, ran out with maybe 12 feet left to cover. Store was out of his color. Special order. Four weeks.

He stared at an almost-finished garage for a month because he didn't buy one extra box.

Keep your leftovers. Throw them in the rafters. Someday a branch falls, a kid throws a baseball, you back into something with the lawnmower. Having matching siding from the same dye lot is worth more than the $200 you "saved" by ordering exact.

You came here for quantities, but let's be real — you want to know the damage.

Quick math for a 16-square project:

• Vinyl: 16 × $400 = ~$6,400 installed
• Hardie: 16 × $800 = ~$12,800 installed

That's a real gap. Whether it's worth it depends on your market, your timeline, and how much you care about what your house looks like. Vinyl is not a crime. Hardie is not a necessity. Make the choice that makes sense for you.

This calculator uses the same math contractors use. Your results might be off slightly once you get into the weeds of exact window sizes and architectural details, but you'll be in the right ballpark — which is the point.

Measure twice. Do the calculator once per wall. Add everything up. Round up, not down.

Buy extra. 10% minimum. 15% if your house has character.

Keep the leftovers. Garage rafters. Attic. Wherever. Future you will need them.

Go get your siding.