Siding Calculator

Calculate how many squares and boxes of vinyl siding you need from your house dimensions, plus starter strip, J-channel and corner posts, minus doors and windows.

By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.

Quick answer: To estimate siding, multiply the house perimeter by the wall height, add the gable triangles, subtract doors and windows, and divide by 100 for squares. A 40 x 30 ft house with 9 ft walls, two 6 ft gables and 120 sq ft of openings has 1,320 sq ft of wall, or 14.5 squares with 10% waste, which is 8 boxes of vinyl siding.

Your measurements

One wall: area is wall length times height, minus each door and window.

House lengthftHouse widthftThe side the gables are on.Wall heightftFrom the bottom of the siding to the eave. Use 18 to 20 ft for two stories, which take 20 ft corner posts to avoid a splice.Gable endsTriangular wall sections above the eave line. 2 for a gable roof, 0 for a hip roof.Gable heightftFrom the eave line to the peak.Doors and windows areasq ftTotal area of all openings. A typical window is 12 to 15 sq ft, an entry door 20 sq ft, a garage door 112 sq ft.Number of openingsUsed for J-channel: about 15 ft per opening.Waste allowance%10% for a simple box, 15% with many gables and openings. Rake cuts on gables run 15 to 20% on their own, and 12 ft panels on 14 ft walls leave 2 ft stubs.

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Siding needed14.5 squaresAll results

Results

Siding needed: 14.5 squares; 1,320 sq ft of wall plus 10% waste
Vinyl siding boxes: 8 boxes; One box covers 2 squares (200 sq ft)
Starter strip: 140 ft; House perimeter; 12 pieces at 12 ft
J-channel: 120 ft; About 15 ft per opening; 10 pieces at 12 ft, plus about 65 ft along the gable rakes
Corner posts: 36 ft; 4 corners x wall height; 4 posts at 10 ft

Siding formula

Wall area = 2 x (Length + Width) x Wall height
Gable area = Gables x (Width x Gable height / 2)
Squares = (Wall area + Gable area - Openings) x (1 + waste %) / 100
Boxes = Squares / 2, rounded up;  Starter strip = Perimeter;  Corner posts = 4 x Wall height

Worked example

A 50 x 28 ft ranch with 8 ft walls, two gables 5 ft high, 200 sq ft of doors and windows in 10 openings: perimeter = 2 x (50 + 28) = 156 ft, x 8 = 1,248 sq ft. Gables: 2 x (28 x 5 / 2) = 140 sq ft. Net area = 1,248 + 140 - 200 = 1,188 sq ft. With 10% waste that is 1,307 sq ft, or 13.1 squares, so buy 7 boxes of vinyl siding.

Trim: 156 ft of starter strip (13 pieces of 12 ft), 10 x 15 = 150 ft of J-channel (13 pieces), and 4 x 8 = 32 ft of corner post, which is 4 posts at 10 ft.

Quick reference

Siding squares by house size (9 ft walls, no gables, before openings, 10% waste)
House footprint	Perimeter	Wall area	Squares	Boxes
30 x 24 ft	108 ft	972 sq ft	10.7	6
40 x 30 ft	140 ft	1,260 sq ft	13.9	7
50 x 30 ft	160 ft	1,440 sq ft	15.8	8
60 x 32 ft	184 ft	1,656 sq ft	18.2	10
40 x 30 ft, two story (18 ft)	140 ft	2,520 sq ft	27.7	14
50 x 30 ft, two story (18 ft)	160 ft	2,880 sq ft	31.7	16

How to measure a house for siding

Measure the length of each wall at the ground and add them up for the perimeter. Then multiply by the height from the bottom of the siding to the eave. For each gable, multiply the width of the gable wall by the height from the eave line to the peak and divide by 2. Add the wall and gable areas, subtract large openings like garage doors, picture windows and entry doors, and divide by 100 to get squares.

Waste on vinyl comes from rake cuts and panel length. Every course on a gable ends in an angled cut whose offcut only fits the mirror spot on the opposite gable. Gable area runs 15 to 20 percent against 10 on straight walls. A 14 ft wall takes a 12 ft panel plus a 2 ft piece with a lap. Some lines come 16 ft 8 in or 20 ft for fewer laps. Leave out walls covered by a porch roof or brick veneer.

Trim and accessories

Starter strip equals the perimeter. Corner posts come 10 and 20 ft; a two-story wall takes 20 ft posts or a 3/4 in lap. J-channel wraps every window and door, runs the gable rakes and any eave where siding meets soffit. Fifteen feet per opening is a fair average; the rake length in the note comes from the gable width and height.

Vinyl hangs loose. Nail in the center of the slot every 16 in with 1-1/2 in aluminum or galvanized roofing nails, straight and stopped 1/32 in short so the panel slides. Leave 1/4 in at every J-channel and corner post, 3/8 in below 40 degrees. Cut panels under windows and at the top course go into utility trim with a snap-lock punch, never face-nailed.

Fiber cement and engineered wood siding are sold by the piece rather than the box. Convert squares to pieces using the exposure and length of the board: a 12 ft board with a 7 in exposure covers 7 sq ft.

What this calculator leaves out

Housewrap (IRC R703.2), a 9 x 100 ft roll covering 900 sq ft, plus seam tape. Flashing tape at every window and door, sill then sides then head, with the wrap lapped over the head (R703.4). About 1 lb of 1-1/2 in roofing nails per square, utility trim, mounting blocks for lights and outlets, inside corner posts and soffit and fascia. Fanfold foam, tear-off, the dumpster and any permit.

Mistakes that cost money

Nails driven tight: the panel buckles the first hot day; leave 1/32 in under the head and center the nail in the slot.
Panels cut tight into J-channel: vinyl grows 1/2 in over 12 ft and bows; leave 1/4 in at each stop, 3/8 in under 40 degrees.
Siding over bare sheathing: vinyl is not watertight; IRC R703.2 requires a water-resistive barrier and R703.4 flashing at every window and door head.
Ten percent waste on gable walls: every course on the rake ends in an angled cut and the offcut rarely fits; figure 15 to 20%.
Face-nailing the cut panel under a window: the heads show and the panel splits; use utility trim and a snap-lock punch.
Butting 10 ft corner posts on a two-story wall: the joint opens in winter; order 20 ft posts or lap the upper over the lower.

Key facts

Siding is sold by the square (100 sq ft). A box of vinyl siding covers 2 squares, and a typical box holds 24 panels 12 ft long.
Standard vinyl panels are 12 ft long with an 8 in or double 4 in exposure; J-channel, starter strip and corner posts come in 10 or 12 ft lengths.
A 3 x 5 ft window is 15 sq ft and an entry door is about 20 sq ft. Many estimators skip subtracting openings under 10 sq ft and count them as waste.
Vinyl siding expands and contracts up to 1/2 in over a 12 ft panel between winter and summer, so panels are nailed loosely with a 1/4 in gap at every stop.

Frequently asked questions

How many squares of siding do I need for a 2,000 sq ft house?

Floor area does not tell you wall area. A 40 x 50 ft single story with 9 ft walls has about 1,620 sq ft of wall plus gables, roughly 16 to 18 squares before subtracting openings. Measure the walls.

How many squares are in a box of vinyl siding?

Two squares, or 200 sq ft. A typical box holds 24 panels 12 ft long, so a 14.5 square job needs 8 boxes.

Do you subtract windows and doors when estimating siding?

Subtract large openings like garage doors and picture windows. Small windows are often left in as part of the waste allowance since the cut pieces around them are rarely reusable.

Do I need housewrap under vinyl siding?

Yes. Vinyl sheds most water but is not watertight. IRC R703.2 requires a water-resistive barrier such as housewrap or #15 felt over the sheathing, lapped shingle-style and taped at the seams. Windows and doors get flashing tape at the sill, sides and head in that order (R703.4), with the wrap lapped over the head flashing. On a re-side, replace torn wrap and add it where there is none.

Sources and references

Vinyl Siding Installation Manual (Polymeric Exterior Products Association (formerly Vinyl Siding Institute))
Vinyl siding product lines and profiles (CertainTeed)
Chapter 7 Wall Covering, 2021 IRC (ICC)

Next steps for this project

The usual order for a roofing & siding project. See all roofing & siding calculators.

Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.