How do I figure out how many squares of siding I need?

Add up the area of the walls (length × height), add each gable end (½ × width × rise), take off the doors and windows, then divide by 100 sq ft, because a square is 100 sq ft. Add 10% for waste. The example house has 1,485 sq ft, so 1,485 × 1.10 ÷ 100 = 16.34 squares, which you order as 17 squares or, by the box, 9 boxes.

How many squares are in a box of vinyl siding?

Most vinyl siding is packed 2 squares (200 sq ft) to a carton, which is the calculator’s starting value, but it varies by maker and profile: some profiles pack 1 square (100 sq ft). The carton, and the data sheet for your profile, gives the true coverage. Change Squares per box to match.

How do I calculate the area of a gable?

A gable end is a triangle: ½ × the width of the wall × the rise from the top of the wall to the ridge. A 30 ft wide gable on a 6/12 roof rises 30 ÷ 2 × 6 ÷ 12 = 7.5 ft, so its area is ½ × 30 × 7.5 = 112.5 sq ft; two of them are 225 sq ft. The table of gable areas shows the area for other widths and pitches. The gable wall below the triangle is part of your wall length × height.

How much waste should I add for vinyl siding?

About 10% is the figure installers and makers commonly give for a plain house, and this calculator starts there. A house with many gables, windows, or short wall sections cuts more, so there is a 15% option; that figure is an estimate, not a maker’s number. Panels are cut to length at every window, corner and wall end, and the offcut is used where it fits. Buying one box more is cheaper than a second order from a different dye lot, since siding color can vary between runs.

Do I subtract windows and doors?

Yes, enter each as an opening. On the example house, eight 3 × 4 ft windows, two 3 × 6.7 ft doors and a 9 × 7 ft garage door take off 199.2 sq ft, leaving 1,285.8 and 8 boxes instead of 9. Each opening also needs J-channel around it, which the calculator adds: 27 sticks in all instead of 12. The waste percentage covers the cuts around them.

How much J-channel and starter strip do I need?

Starter strip runs along the base of the whole building, so its length is the total wall length: 140 ft is 12 sticks of 12 ft 6 in. J-channel goes around each door and window, up the rake of each gable and, where there is no frieze board, under the eaves. Without openings, the example house needs 147 ft of it for its two gables (67 ft of rake) and the eaves (80 ft): 12 sticks. With the eaves taken off the list it is 6. These are planning figures; your trim details may differ.

What is not counted here?

Corner posts, undersill and finish trim, soffit and fascia, flashing, house wrap, nails and the sheathing under the siding are not included. Corner posts go on every outside corner, so count them on your house and match their length to your wall height. Fastener spacing is set by the maker’s instructions.

Does this work for fiber cement, wood or metal siding?

The area part does: net area, squares and waste work for any siding sold by the square. The box is vinyl-specific, so set Squares per box to what your product holds, or ignore the box count and use the squares. J-channel and starter strip are vinyl accessories; fiber cement and wood use different trim and flashing.

Siding Calculator: Squares and Boxes of Vinyl Siding

A house with 140 ft of wall all the way round, 9 ft high, with two gable ends 30 ft wide and 7.5 ft tall (a 6/12 roof), has 1,485 sq ft of siding to cover: 1,260 sq ft of wall plus 225 sq ft of gables. With 10% waste that is 16.34 squares, or 9 boxes at the usual 2 squares (200 sq ft) a box. Add 12 sticks of starter strip and 12 sticks of J-channel (12 ft 6 in each) for the base, the rakes and the eaves, before any doors and windows, which come off the area and add J-channel around each. A square is 100 sq ft; a gable is ½ × width × rise.

Figures based on the sources listed belowUpdated 2026-10-07How we calculate

Total wall length (all the way round)

Wall height

Waste

Standard (10%)Many gables, openings or short walls (15%)Custom

Gable ends

Triangular walls under the roof ridge. A simple gable roof has 2; a hip roof has none. Leave 0 to skip them.

Gable width

The width of the wall the gable sits on, along its base. The same for every gable here.

Gable rise (height of the triangle)

From the top of the wall to the ridge. A 6/12 roof on a 30 ft wide gable rises 7.5 ft: half the width × 6 ÷ 12.

Squares per box

A square is 100 sq ft. Most vinyl siding comes 2 squares (200 sq ft) to a carton, but some profiles pack 1 or 1.5; read the carton or the product data sheet.

J-channel under the eavesSiding is usually finished under the eaves with J-channel (or a frieze board and undersill trim). The eave run is the wall length less the gable walls.

Price per box (optional)

Buy 9 boxes

1,485 sq ft + 10% waste = 1,633.50 sq ft

Squares to order (100 sq ft each, with waste): 17 squares, the walls themselves are 14.85 squares
Gable ends: 2 gables, 225 sq ft in all
Starter strip (12 ft 6 in sticks): 12 sticks (≈ 140 ft)
J-channel (12 ft 6 in sticks): 12 sticks (≈ 147.1 ft)

How this number is calculated

1,485 sq ft + 10% waste = 1,633.50 sq ft ÷ 200 sq ft per box = 9 boxes

Shopping list

Vinyl siding J-channel
Vinyl siding starter strip
Siding nail hole slot punch
Vinyl siding zip tool (unlocking tool)
Aviation snips
Galvanized siding nails (1-1/4 in)
Chalk line

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Squares and boxes by wall area

For a net wall area (gables included, openings taken off), with 10% waste. Boxes at 2 squares (200 sq ft) each, for 10% and 15% waste. Worked by this calculator.
Net area	Squares with 10% waste	Boxes at 10%	Boxes at 15%
500 sq ft	5.5	3	3
800 sq ft	8.8	5	5
1,000 sq ft	11	6	6
1,200 sq ft	13.2	7	7
1,500 sq ft	16.5	9	9
2,000 sq ft	22	11	12
2,500 sq ft	27.5	14	15
3,000 sq ft	33	17	18

Gable area by width and roof pitch

Area in sq ft of one gable end (½ × width × rise), where the rise is half the width × the pitch ÷ 12. Worked by this calculator, no waste. Multiply by the number of gables.
Gable width	4/12 pitch	6/12 pitch	8/12 pitch	12/12 pitch
16 ft	21.3	32	42.7	64
20 ft	33.3	50	66.7	100
24 ft	48	72	96	144
28 ft	65.3	98	130.7	196
30 ft	75	112.5	150	225
32 ft	85.3	128	170.7	256
36 ft	108	162	216	324

Area and J-channel around common openings

The siding area an opening takes off and the J-channel that goes around its full perimeter, 2 × (width + height), in ft and in 12 ft 6 in sticks (estimate). Worked by this calculator.
Opening	Area (sq ft)	J-channel (ft)	Sticks
Window 3 × 4 ft	12	14	2
Window 3 × 5 ft	15	16	2
Door 3 × 6.7 ft (36 × 80 in)	20.1	19.4	2
Sliding door 6 × 6.7 ft	40.2	25.4	3
Garage door 9 × 7 ft	63	32	3
Garage door 16 × 7 ft	112	46	4

Methodology & assumptions

Total wall length is the distance all the way round the house, and the wall height is the height from the foundation or the bottom of the starter strip to the soffit; a rectangular house of 40 × 30 ft has 140 ft of wall. Wall area is length × height. Each gable is a triangle: ½ × width × rise, where the width is the wall below it and the rise is the height from the top of the wall to the ridge; the gables are added to the wall area. Doors and windows (and garage doors) are measured width × height and subtracted. Entering every opening is the careful method; the waste percentage covers the cuts around them. The net area is multiplied by 1 plus the waste (10%, or 15% for a house with many gables, openings or short walls) and divided by 100 sq ft for squares. Boxes = net area × (1 + waste) ÷ the coverage of a box, rounded up. The coverage of a box is an input: the usual carton holds 2 squares, 200 sq ft, but panel profile and maker vary, so read your carton or data sheet. A carton is not cut: you buy whole boxes, so the last one is often partly used, and you should buy a spare box of the same lot because colors vary between production runs. Starter strip runs along the base of the building: its length is the total wall length. J-channel goes around every door and window (the full perimeter, 2 × (width + height) of each opening), along both sloped rake edges of each gable (2 × √((width ÷ 2)² + rise²) per gable) and, if you pick it, under the eaves, which is the wall length less the base of each gable wall. Both are sold in sticks of about 12 ft 6 in, rounded up; no waste is added, and corner posts, undersill trim, soffit and fasteners are not counted. These accessory lengths are an estimate; flashing, trim and house wrap are separate. The metric toggle shows lengths in m and areas in m².

CertainTeed, Vinyl and Polymer Siding Installation Guide (the estimating form and the accessory sections): starter strip measured along the base of the building, J-channel around doors and windows, under eaves and at the rake edges of gables, accessories in 12 ft 6 in sticks
CertainTeed, Estimating and Installing Vinyl Siding: measuring walls, gables and openings and adding about 10% for waste
Vinyl Siding Institute (VSI), Installation Quick Tips: starter strip along the base, J-channel at windows, doors and the sloped eaves of gable ends
Typical carton: vinyl siding is usually packed 2 squares (200 sq ft) to a box, though some profiles pack 1 square. This is a typical figure from retailer and installer guides, not one maker’s data sheet: check the carton for your profile (the calculator takes squares per box as an input)

How to calculate how much vinyl siding you need

Measure the walls. Add up the length of every wall all the way round the house, and measure the wall height from the base of the siding to the soffit.
Measure the gables. For each gable end, measure the width of the wall below it and the height of the triangle from the top of the wall to the ridge. The area is half the width times the rise.
Subtract openings. Measure each door, window and garage door, width times height, and subtract the total from the area.
Add waste and convert to squares. Add 10% for cuts and waste, divide by 100 sq ft for squares, and divide by the squares in a box (usually 2) for boxes, rounding up.
Count the trim. Starter strip along the base of the walls, and J-channel around openings, up the gable rakes and under the eaves, divided by 12.5 ft per stick, rounded up.

Worked examples

Project	Result
140 ft of wall, 9 ft high, two gables 30 ft wide and 7.5 ft rise, 10% waste, 2 squares a box	1,485 sq ft + 10% → 9 boxes, 17 squares, 12 starter and 12 J-channel sticks
The same house with eight 3 × 4 ft windows, two 3 × 6.7 ft doors and a 9 × 7 ft garage door	1,285.8 sq ft + 10% → 8 boxes, 15 squares, 12 starter and 27 J-channel sticks
A 160 ft hip-roof ranch, 9 ft walls, no gables, ten windows and two doors, 15% waste	1,279.8 sq ft + 15% → 8 boxes, 15 squares, 13 starter and 28 J-channel sticks
A garage: 80 ft of wall, 8 ft high, two gables 20 ft wide and 5 ft rise, a profile packed 1 square a box	740 sq ft + 10% → 9 boxes, 9 squares, 7 starter and 7 J-channel sticks

Frequently asked questions

How do I figure out how many squares of siding I need?: Add up the area of the walls (length × height), add each gable end (½ × width × rise), take off the doors and windows, then divide by 100 sq ft, because a square is 100 sq ft. Add 10% for waste. The example house has 1,485 sq ft, so 1,485 × 1.10 ÷ 100 = 16.34 squares, which you order as 17 squares or, by the box, 9 boxes.
How many squares are in a box of vinyl siding?: Most vinyl siding is packed 2 squares (200 sq ft) to a carton, which is the calculator’s starting value, but it varies by maker and profile: some profiles pack 1 square (100 sq ft). The carton, and the data sheet for your profile, gives the true coverage. Change Squares per box to match.
How do I calculate the area of a gable?: A gable end is a triangle: ½ × the width of the wall × the rise from the top of the wall to the ridge. A 30 ft wide gable on a 6/12 roof rises 30 ÷ 2 × 6 ÷ 12 = 7.5 ft, so its area is ½ × 30 × 7.5 = 112.5 sq ft; two of them are 225 sq ft. The table of gable areas shows the area for other widths and pitches. The gable wall below the triangle is part of your wall length × height.
How much waste should I add for vinyl siding?: About 10% is the figure installers and makers commonly give for a plain house, and this calculator starts there. A house with many gables, windows, or short wall sections cuts more, so there is a 15% option; that figure is an estimate, not a maker’s number. Panels are cut to length at every window, corner and wall end, and the offcut is used where it fits. Buying one box more is cheaper than a second order from a different dye lot, since siding color can vary between runs.
Do I subtract windows and doors?: Yes, enter each as an opening. On the example house, eight 3 × 4 ft windows, two 3 × 6.7 ft doors and a 9 × 7 ft garage door take off 199.2 sq ft, leaving 1,285.8 and 8 boxes instead of 9. Each opening also needs J-channel around it, which the calculator adds: 27 sticks in all instead of 12. The waste percentage covers the cuts around them.
How much J-channel and starter strip do I need?: Starter strip runs along the base of the whole building, so its length is the total wall length: 140 ft is 12 sticks of 12 ft 6 in. J-channel goes around each door and window, up the rake of each gable and, where there is no frieze board, under the eaves. Without openings, the example house needs 147 ft of it for its two gables (67 ft of rake) and the eaves (80 ft): 12 sticks. With the eaves taken off the list it is 6. These are planning figures; your trim details may differ.
What is not counted here?: Corner posts, undersill and finish trim, soffit and fascia, flashing, house wrap, nails and the sheathing under the siding are not included. Corner posts go on every outside corner, so count them on your house and match their length to your wall height. Fastener spacing is set by the maker’s instructions.
Does this work for fiber cement, wood or metal siding?: The area part does: net area, squares and waste work for any siding sold by the square. The box is vinyl-specific, so set Squares per box to what your product holds, or ignore the box count and use the squares. J-channel and starter strip are vinyl accessories; fiber cement and wood use different trim and flashing.

Handy tools

Slope Calculator: Turn a roof pitch such as 6/12 into the rise of a gable: half the width × the pitch ÷ 12.
Feet and Inches Calculator: Add up tape-measure readings in feet, inches and fractions into the decimal feet the fields take.