How do I measure a house for siding?

Measure each wall's length and height, multiply to get its area, add the gable areas, then subtract windows and doors. Add about 10% for waste and divide by 100 to get squares. Measure trim separately in linear feet.

How do you measure a gable for siding?

Multiply the width of the gable's base by its height at the peak, then divide by two. A gable 28 ft wide and 7 ft tall is 28 × 7 ÷ 2 = 98 sq ft. If you cannot reach the peak, calculate the rise from the roof pitch.

Do I measure windows and doors for siding?

Yes. Subtract each opening's area from the gross wall area because siding does not cover it. Many installers subtract only larger openings and leave small ones in as a built-in waste allowance.

How do I measure siding I already have on the house?

Measure the exposed height of one course, called the exposure, and compare it with the product you want. Your existing exposure tells you the profile, but you still need wall and gable areas to work out the quantity.

Can I estimate siding from my home's square footage?

Not reliably. Floor area and wall area are different things, and ceiling height, roof shape and number of stories change the result. Measure the actual walls for anything you plan to order.

How to Measure a House for Siding (Walls, Gables and Openings)

Measuring for siding is mostly rectangles and triangles. If you can multiply two numbers and divide by two, you can take an accurate measurement in an afternoon. The steps below work for vinyl, fiber cement, wood and metal because every product is ordered from the same starting number: net wall area.

You will need a tape measure (a 25 ft one is fine, a 100 ft one is better), a notepad or phone, a helper for tall walls, and a ladder used safely. A photo of each wall next to your notes helps later.

Step 1: Sketch the house

Draw a rough plan of the house and label each wall: front, back, left, right, plus any bump-outs, garages or porches. A sketch keeps you from counting a wall twice or skipping one.

Step 2: Measure each wall

For every wall, measure its length along the ground and its height from the bottom edge of where the siding will start up to the underside of the eave or soffit. Multiply length by height.

A wall 28 ft long and 9 ft tall is 28 × 9 = 252 sq ft.

If a wall has steps, a two-story section next to a one-story section, or a bump-out, split it into separate rectangles and measure each one. Add them together afterward.

Step 3: Measure the gables

A gable is the triangle of wall under a peaked roof. Its area is base × height ÷ 2, where the base is the width across the bottom and the height is the vertical rise to the peak.

A gable 28 ft wide and 7 ft tall is 28 × 7 ÷ 2 = 98 sq ft.

Not comfortable measuring up at the peak? Work out the rise from the roof pitch. A 6/12 pitch rises 6 inches for every 12 inches of horizontal run. Half the gable width is the run, so on a 28 ft wide gable the run is 14 ft and the rise is 14 × 6 ÷ 12 = 7 ft, matching the example above.

Gambrel (barn-style) gables are two trapezoids stacked together; measure the lower and upper sections separately.

Step 4: Add walls and gables

Total every wall and every gable. This is your gross area. Keep separate subtotals per wall so you can double-check your math later.

Step 5: Measure and subtract openings

Measure the width and height of each window, door and garage door, multiply them, and subtract the total from your gross area. What remains is your net area.

Six windows at 3 × 4 ft, a 3 × 6.67 ft entry door and a 9 × 7 ft garage door remove 72 + 20 + 63 = 155 sq ft.

Some pros skip small openings such as a tiny basement window because the siding cut out of them ends up as useful offcuts. When in doubt, subtract them. The waste allowance in the next step covers the difference.

Step 6: Measure trim in linear feet

Trim is bought by length, not area, so measure it separately:

Outside corners: the height of each corner. Use the corner post calculator.
Windows and doors: the perimeter of each opening, for J-channel or trim. Use the J-channel calculator.
Bottom of the wall: total wall length for starter strip. Use the starter strip calculator.

Step 7: Add waste and convert to squares

Cuts at corners, openings and rooflines, plus the odd damaged piece, mean you need more than net area. Ten percent suits a simple rectangular house; complex homes with several gables or dormers often need 15% or more. See siding waste factor for how to choose.

Multiply net area by (1 + waste) and divide by 100 for squares. For 800 sq ft net at 10% waste: 800 × 1.10 ÷ 100 = 8.8 squares.

Quick check with perimeter × height

To catch big mistakes, compare your wall total with a shortcut: add up the distance around the house (the perimeter) and multiply by the wall height. A 28 × 20 ft rectangle with 9 ft walls has 96 ft of perimeter, and 96 × 9 = 864 sq ft. If your detailed wall total is far from that, recheck a measurement.

Let the calculator do the arithmetic

Enter each wall, gable and opening into the Siding Calculator and it totals the area, adds waste, and converts to squares and product units. If you already have net area, the Siding Squares Calculator converts it directly.