Pick the siding material before you measure a single wall. Vinyl, wood and fiber cement all sell by the square, but they install at different speeds, waste out at different rates and last for different lengths of time. The wall area is the easy part. Choosing what goes on that wall is the decision that shapes the next thirty years of the house.
Once the material is chosen, the math is straightforward. Siding is measured in squares, and one square covers 100 square feet. Measure the perimeter, multiply by the wall height, pull out the doors and windows, add a tenth for waste, and divide by 100.
How a square works
Contractors talk about squares the way painters talk about gallons, because the numbers stay small. A 100 foot perimeter house with 10 foot walls starts at 1000 square feet of wall area, which is 10 squares. Deduct three doors at 20 square feet each and eight windows at 15, add 10 percent waste, and you are ordering around 9 squares.
Vinyl siding arrives in boxes that cover a set number of squares per pack, often 2 squares per two-box bundle. Fiber cement planks are priced by the square or by the linear foot, and wood lap siding follows the same pattern. The conversion to 100 square feet per square is what keeps all three comparable on paper.
Vinyl versus wood versus fiber cement
Vinyl is the budget and DIY favorite. It clicks together, needs no paint, and goes up fast, which is why it covers so many American suburban homes. The tradeoff is that it fades in strong sun, can crack in a deep freeze, and dents when a ladder leans against it the wrong way. It also cannot really be repainted once the color dulls.
Wood siding, whether cedar lap or shingles, is the look people pay premium for. It breathes, it ages gracefully, and it can be restained whenever the mood changes. The cost is maintenance, because wood needs staining or painting every handful of years and it is vulnerable to rot and insects where water pools.
Fiber cement, sold under names like HardiePlank, sits between the two. It looks like wood, it resists fire, rot and bugs, and it holds paint for 15 years at a stretch. The price is roughly double vinyl, and the weight makes it a two-person install. Over the life of the house it usually wins on total cost.
Measure the walls
Walk the full perimeter of the house and add every side, including the little bump-outs over the garage and the bay window. Multiply by the wall height, which is usually 8 to 10 feet on a single story. Do not forget that a two-story house has taller walls on each side, not a second copy of the first floor.
Pull out the openings. Budget 20 square feet per exterior door and 15 per window. These estimates are close enough that you will not overbuy a whole square, and the waste factor absorbs the few inches you guessed wrong.
Gables and waste
The calculator covers the rectangular parts of the walls. The triangular gable ends above the garage and the second floor are a separate shape. Add roughly half the gable width times its height for each gable, or if you would rather not measure triangles, push the waste factor from 10 percent up to 15 percent.
Corners, windowsills and the starter strip along the bottom all eat a little material that does not show up in the wall area. That is exactly what the waste number pays for, and skipping it is how a siding job ends with one box short on the last wall.
Cost and the bottom line
Once you know the squares, multiply by the price per square for the material you chose. Vinyl runs the cheapest per square, wood sits in the middle, and fiber cement lands on top. Add labor if you are not doing it yourself, and remember that the underlayment, flashing and trim are separate line items that the square count does not include.
A 100 by 10 foot house with ordinary openings lands around 9 squares after waste. Order 9 and a half or 10 to be safe, because siding from a second run can come in a slightly different shade, and mismatched panels on a finished wall are impossible to hide.
See also the paint calculator for the coats that finish fiber cement and the shingle calculator for the roof above it.
Siding Calculator
One square covers 100 square feet, so measure the wall perimeter, deduct openings and add 10 percent waste before choosing the material.
How to use
- Walk the house perimeter in feet across all four walls
- Enter the wall height, typically 8 to 10 feet
- Count exterior doors and windows to deduct the openings
- Pick vinyl, wood or fiber cement and enter the price per square
- Read the total squares and the estimated project cost
Supported formats and limits
- One square of siding covers 100 square feet
- Each exterior door deducts about 20 square feet
- Each window deducts about 15 square feet
- A 10 percent waste factor is included
Examples
A 100 foot perimeter at 10 foot walls with three doors and eight windows needs about 9 squares after waste.Common errors
- Perimeter must be a positive number
- Wall height should sit between 6 and 16 feet
- Price per square should be greater than zero
Privacy and browser support
All calculations run locally in your browser and nothing is uploaded.
FAQ
What is a square of siding?
One square covers 100 square feet of wall. Siding is sold by the square, and vinyl bundles often cover 2 squares per pack.
How many squares does a 1500 square foot house need?
Wall area is not floor area. A single-story 1500 square foot house usually carries 1500 to 1800 square feet of wall, or 15 to 18 squares.
Vinyl, wood or fiber cement?
Vinyl is cheap and DIY-friendly but fades and cracks. Fiber cement lasts 30 to 50 years and holds paint. Wood looks rich but needs ongoing paint.
Do I add anything for gables?
Yes. Add half the gable width times its height for each gable end, or simply bump the waste factor up to 15 percent.
How much waste should I expect?
Plan on 10 percent for simple rectangular walls, and closer to 15 percent when gables, corners and lots of windows are involved.
Is fiber cement worth the extra cost?
It costs about twice vinyl up front but lasts decades longer and shrugs off fire, rot and insects, which matters over the life of the house.