Siding Calculator
How much siding do I need for a 40 x 30 ft house?
With 8 ft walls, two 30 ft gables 6 ft tall, 2 doors and 10 windows, the net area is 1,108 sq ft. Add 10% waste and you need 1,218.8 sq ft, or 12.19 squares: about 7 boxes of vinyl at a typical 2 squares per box, or 153 double 4 in vinyl panels 12 ft long.
This siding calculator adds up the area of every wall and gable on your house, subtracts the doors and windows, and adds a waste allowance. It returns the net square footage, the square footage to buy, and the number of siding squares (100 sq ft each).
For vinyl it also estimates boxes, using a typical carton of 2 squares, and for vinyl or lap siding it counts 12 ft panels or planks from the exposure you choose. The defaults show a 40 × 30 ft single-story house so you can see a full result before you type anything.
Enter your details
How to Use the Siding Calculator
- 1
Enter each wall
Add one row per wall with its length and height in feet, measured from the bottom of the siding to the soffit. Use the + Add a wall button for bump-outs and garages.
- 2
Add the gables
For each triangular end wall, enter the base width and the height from the top of the wall to the peak. Remove the gable rows if the house has a hip roof.
- 3
Subtract openings
Enter the number of doors and windows. The defaults are 21 sq ft per door (3 × 7 ft) and 15 sq ft per window (3 × 5 ft). Switch on the custom total if you have measured the openings yourself.
- 4
Pick the siding and waste
Choose double 4 in vinyl (8 in exposure), double 5 in vinyl (10 in), 7 in lap siding or a custom exposure, set the panel length (12 ft by default) and the waste percentage (10% by default).
How the siding calculator works
Walls are rectangles, so each one is length times height. Gables are triangles, so each one is half the base times the peak height. The calculator adds them up, subtracts the openings to get the net area, then multiplies by 1 plus the waste percentage.
Siding is sold and quoted by the square, which is 100 sq ft of wall coverage. Panel and plank counts use the exposure, the part of each course that shows once installed. A 12 ft panel with an 8 in exposure covers 8 ÷ 12 × 12 = 8 sq ft, so the area with waste is divided by 8 and rounded up.
Net sq ft = Σ(wall length × height) + Σ(gable base × peak height ÷ 2) − openings
Sq ft to buy = net × (1 + waste % ÷ 100)
Squares = sq ft to buy ÷ 100
Panels = sq ft to buy ÷ (exposure in ÷ 12 × panel length ft), rounded up
Vinyl boxes = squares ÷ 2, rounded up (typical carton)Worked example: a 40 × 30 ft ranch
- Walls: 2 × (40 × 8) + 2 × (30 × 8) = 640 + 480 = 1,120 sq ft.
- Gables: two 30 ft wide, 6 ft tall: 2 × (30 × 6 ÷ 2) = 180 sq ft. Gross area 1,300 sq ft.
- Openings: 2 doors × 21 + 10 windows × 15 = 192 sq ft. Net area 1,108 sq ft.
- Add 10% waste: 1,108 × 1.10 = 1,218.8 sq ft, or 12.19 squares.
- Vinyl boxes at 2 squares each: 12.19 ÷ 2 = 6.09, so 7 boxes.
- Double 4 in panels (8 sq ft each): 1,218.8 ÷ 8 = 152.4, so 153 panels. Double 5 in (10 sq ft each) needs 122; 7 in lap planks (7 sq ft each) need 175.
- Starter strip: 140 ft of wall ÷ 12 ft = 12 pieces (a rough figure the tool shows separately).
Siding for common house sizes
Four walls only, no gables, nothing subtracted for openings, 10% waste. Panels are 12 ft double 4 in vinyl. Add your gables from the next table and subtract openings for a tighter figure.
| Footprint | Wall height | Wall sq ft | With 10% | Squares | Vinyl boxes | D4 panels |
|---|---|---|---|---|---|---|
| 30 × 24 ft | 8 ft | 864 | 950.4 | 9.50 | 5 | 119 |
| 40 × 30 ft | 8 ft | 1,120 | 1,232 | 12.32 | 7 | 154 |
| 50 × 30 ft | 9 ft | 1,440 | 1,584 | 15.84 | 8 | 198 |
| 60 × 40 ft | 9 ft | 1,800 | 1,980 | 19.80 | 10 | 248 |
Gable area and panel coverage
Carton coverage varies by brand and profile. Two squares per box is common for double 4 in vinyl, but always check the label before you order.
- Double 4 in vinyl, 8 in exposure, 12 ft panel: 8 sq ft per panel, 12.5 panels per square.
- Double 5 in vinyl, 10 in exposure, 12 ft panel: 10 sq ft per panel, 10 per square.
- Lap siding at 7 in exposure, 12 ft plank: 7 sq ft per plank, about 14.3 per square.
- Many vinyl panels are 12 ft 6 in rather than 12 ft. Enter 12.5 as the panel length if that is what you are buying.
| Gable base | Peak height | Area (sq ft) |
|---|---|---|
| 24 ft | 4 ft | 48 |
| 24 ft | 6 ft | 72 |
| 30 ft | 6 ft | 90 |
| 30 ft | 7.5 ft | 112.5 |
| 36 ft | 9 ft | 162 |
Edge cases the simple formula misses
- Trim is separate. J-channel around windows and doors, outside and inside corner posts, undersill trim, soffit and fascia are not in the area figure. The tool only adds a rough starter strip count from total wall length.
- Dormers, bay windows and bump-outs: add each face as its own wall or gable row. Small triangles over porch roofs add up.
- Large openings such as garage doors: use the custom total so you do not subtract a 16 × 7 ft door as 21 sq ft.
- Steep or complex gables and lots of corners create more offcuts. Go to 12 to 15% waste on cut-up houses; 10% suits plain rectangles.
- If you are also redoing the roof, measure it with the roofing calculator. Painting wood or fiber cement siding instead? Use the wall area here in the paint calculator.
When to call a professional
Siding a single-story house with plain walls is a common DIY job. Get a contractor involved if the work is above a second story, if the sheathing is soft or rotted, if you find moisture behind the old siding, or if the house may have lead paint or asbestos siding, which needs testing and special handling before removal. Fiber cement also has its own cutting dust precautions and fastening schedule, so follow the manufacturer installation guide, which may affect your warranty.
Features
- Any number of rectangular walls and triangular gables
- Subtracts doors (21 sq ft) and windows (15 sq ft), or a custom total
- Net area, area with waste (default 10%) and siding squares
- Vinyl boxes at a typical 2 squares per box
- Panel or plank count for double 4, double 5 or 7 in lap exposure
- Rough starter strip estimate from total wall length
Frequently Asked Questions
How many squares of siding do I need?
Add up the wall and gable area, subtract doors and windows, add about 10% for waste and divide by 100. A 40 × 30 ft house with 8 ft walls, two 30 ft gables 6 ft tall, 2 doors and 10 windows has a net area of 1,108 sq ft, which is 1,218.8 sq ft with waste, or 12.19 squares.
How many boxes of vinyl siding do I need?
Divide the squares (including waste) by the coverage per box and round up. A typical box of double 4 in vinyl covers 2 squares, or 200 sq ft, so 12.19 squares needs 7 boxes. Coverage varies by brand and profile, so check the carton before you order.
How many siding panels are in a square?
Divide 100 by the coverage of one panel. A 12 ft double 4 in vinyl panel has an 8 in exposure and covers 8 sq ft, so a square takes 12.5 panels. A double 5 in panel covers 10 sq ft (10 per square) and a 12 ft lap plank at 7 in exposure covers 7 sq ft (about 14.3 per square).
How do I calculate the siding on a gable?
A gable is a triangle, so multiply the base width by the height from the top of the wall to the peak and divide by 2. A gable 30 ft wide and 6 ft tall is 30 × 6 ÷ 2 = 90 sq ft. Add one gable row per triangular end wall.
Should I subtract windows and doors from siding?
Yes, for normal windows and doors, but keep the 10% waste allowance because the cuts around them create offcuts. The calculator uses 21 sq ft per door and 15 sq ft per window by default. For large openings like garage doors, measure them and use the custom total.
Last reviewed