Siding Calculator
Measure around the house and up to the eaves, add your gables, windows and doors, and pick a siding. You'll get squares to order, cartons or planks, and the trim pieces that go with them.
- Tested formulas
- Feet or metric
- Printable shopping list
2 What to buy
Updates as you type| Wall area | 1,440 sq ft |
|---|---|
| Gable ends | 225 sq ft |
| Garage doors (half their area taken off) | − 56 sq ft |
| Area to side | 1,609 sq ft |
| With extra for cuts and waste | 1,770 sq ft = 17.7 squares |
| Starter strip | 13 pieces (160 ft around the base) |
| J-channel | 24 pieces around windows, doors and gable rakes |
| Utility (undersill) trim | 11 pieces for the top course under the eaves and under windows |
| Corner posts (10 ft) | 4 outside, 0 inside |
| Siding nails | about 16 lb of roofing nails, or 8 lb of aluminum nails |
Ordinary windows and doors aren't taken off the area: the cut-outs end up as waste anyway. The Vinyl Siding Institute only takes off half the area of big openings like garage doors.
Shopping list
Quick answer
Siding squares = (wall area + gable area − half of any garage door) × 1.10 ÷ 100. A house 160 ft around with 9 ft walls and two 30 ft gables needs about 17.7 squares: 9 cartons of double 4" vinyl siding.
Fiber cement planks per square
| Plank width | Exposure | Planks per square |
|---|---|---|
| 5¼" | 4" | 25 |
| 6¼" | 5" | 20 |
| 7¼" | 6" | 17 |
| 8¼" | 7" | 14 |
| 9¼" | 8" | 13 |
| 12" | 10¾" | 9 |
James Hardie's HardiePlank chart, 12 ft planks per 100 sq ft, before waste. Use the calculator above for your exact size.
How siding is measured
Siding is sold by the square, which covers 100 sq ft of wall. Measure around the house for the wall length and multiply by the wall height to the eaves. Each gable end is a triangle: half its width times its height. Add them up, then add about 10% for cuts and waste, as the Vinyl Siding Institute recommends.
Don't take ordinary windows and doors off the area. The pieces you cut out mostly end up as waste, so the deduction and the waste cancel out. For big openings such as garage doors, the Institute takes off half their area.
Worked example: a 160 ft perimeter ranch with two gables
- Walls: 160 × 9 = 1,440 sq ft. Gables: 2 × ½ × 30 × 7.5 = 225 sq ft.
- One 16 × 7 ft garage door takes off half its area, 56 sq ft, leaving 1,609 sq ft.
- Plus 10%: 17.7 squares. Double 4" vinyl comes 2 squares to a carton, so that's 9 cartons.
- Trim: 13 starter strips, 24 pieces of J-channel and 11 of utility trim, all 12'6" long, plus 4 outside corner posts.
The trim pieces
- Starter strip runs around the whole base of the house and locks in the first course.
- J-channel goes around windows and doors and up the sloped rake edges of each gable.
- Utility (undersill) trim holds the cut top course under the eaves and under windows.
- Corner posts come in 10 ft lengths. Taller corners need two, lapped.
Nailing vinyl siding
- Nail horizontal panels every 16 inches at most, and accessories every 8 to 12 inches, per the Vinyl Siding Institute.
- Leave about 1/32 inch between the nail head and the panel. Vinyl expands and contracts and must be able to slide.
- Nails need to reach at least 1¼ inches into solid wood (sheathing plus framing).
Frequently asked questions
How many square feet are in a square of siding?
100 square feet. A carton of double 4" or double 5" vinyl siding usually holds 2 squares, enough for 200 sq ft of wall.
How much extra siding should I buy?
About 10% more than the wall area, as the Vinyl Siding Institute recommends. Houses with many corners, dormers or gables may need more.
Should I subtract windows and doors when measuring for siding?
Not normal-sized ones; the cut-out pieces become waste anyway. The Vinyl Siding Institute takes off half the area of large openings like garage doors and sliding doors.
How long is J-channel?
Most J-channel, utility trim and starter strip is sold in 12 ft 6 in lengths, and corner posts in 10 ft lengths.
Last reviewed 2026-10-23. See how we calculate for our sources and assumptions.