Siding Calculator
Measure around the house and up the wall, subtract the windows and doors, and this calculator gives you the siding in squares and boxes — plus starter strip, J-channel and corner posts, and a cost estimate.
Results
How the siding calculator works
Siding is sold by the square — 100 square feet, the same unit roofers use — and vinyl usually arrives two squares to a box. So the whole job is one area problem: measure the walls, add the gables, take out the big openings, add waste, divide by 100.
Formula: perimeter × wall height + gable area − openings = net area, then net area × (1 + waste%) ÷ 100 = squares.
A gable is a triangle, so its area is ½ × width × rise — the width at the top of the wall and the vertical rise to the peak. Two gables on a 30 ft wide house with a 7.5 ft rise add 225 sq ft, which is well over two squares and easy to forget.
| Opening | Approx. area | J-channel needed |
|---|---|---|
| Standard window | 15 sq ft | ≈ 16 ft |
| Entry door | 21 sq ft | ≈ 17 ft |
| Sliding patio door | 40 sq ft | ≈ 26 ft |
| Garage door (single) | 112 sq ft | ≈ 25 ft |
Ordering tips
- Add 10% waste on a simple rectangular house, 15% with gables and jogs, and up to 20% on a wall with many openings — every window means offcuts.
- Order all your siding from the same production lot. Vinyl color varies slightly between runs, and it shows badly on a long, sunlit wall.
- Trim is priced and counted separately: starter strip around the whole base, J-channel around every opening, undersill at the top, and corner posts at each outside corner.
- Corner posts come in 10 ft lengths, so a 9 ft wall takes one post per corner and a 12 ft wall takes two.
- Doing the roof at the same time? Size it with the roofing calculator, and count the bundles with the shingle calculator.
Frequently asked questions
How many squares of siding do I need?
Multiply the perimeter of the house by the wall height, add the gable triangles, subtract the windows and doors, add 10–15% for waste and divide by 100. A 160 ft perimeter with 9 ft walls, two gables and a dozen openings works out to roughly 16 squares.
How many boxes of vinyl siding is a square?
Most vinyl siding is boxed two squares to a carton, so one box covers 200 sq ft. Some premium and insulated profiles come one square to the box — check the carton before you convert, because getting it wrong doubles or halves your order.
Do I subtract windows and doors from siding?
Yes, for anything sizeable — a standard window is about 15 sq ft and an entry door about 21 sq ft. Many installers only deduct openings larger than roughly 10 sq ft and let the small ones absorb into the waste allowance, which is a safe way to work.
How much waste should I add for siding?
About 10% on a simple rectangular house, 15% when there are gables, jogs and dormers, and up to 20% on a facade with a lot of windows. Offcuts around openings are the main source of waste, so the more cut-up the wall, the higher the figure.