Siding Calculator
This vinyl siding calculator turns your house's footprint, wall height and roof pitch into squares and 2-square boxes — with gable triangles computed for you, openings netted out, and the whole trim system counted: starter strip, J-channel, corner posts and house wrap, plus an installed-cost range.
Price edits are remembered on this device — no account, nothing sent anywhere.
installed = squares × $300–$600 per square, labor included
Estimates only, not quotes. Prices are editable national averages — confirm current pricing and quantities with your supplier before you buy.
How this siding calculator counts squares and boxes
Siding is sold like roofing: by the square, 100 sq ft of wall, with vinyl packed two squares to a box. The wall area everyone can measure is perimeter × wall height; the two pieces people miss are above and inside it. Above: each gable end adds a triangle whose height depends on the roof pitch — a 6/12 pitch on a 30 ft wide house adds 112 sq ft per gable. Inside: windows, doors and garage doors come out, at the same standard allowances our drywall and paint tools use.
The trim system is where first-time orders fall apart, so this calculator counts it in the lengths stores actually sell: starter strip along the base (your perimeter), J-channel around openings and up the gable rakes, 10-ft corner posts per outside corner, and 9 × 100 ft house wrap rolls over the gross wall. None of it is exotic — it is all division — but forgetting the J-channel is the classic second trip to the store.
The installed range prices the job per square with labor included, using editable low/high rates, so the same inputs answer both "what do I buy?" and "what will a crew charge?" — and every price is a labeled national-average estimate you can overwrite with a local quote.
The formula
Worked example: siding for a 40×30 ft house
Default inputs: a 40 × 30 ft single-story footprint, 9 ft walls, two gable ends at 6/12 pitch, 8 windows, 2 doors, 1 double garage door, 4 outside corners, 10% waste, house wrap included.
- 1. Perimeter · wall2 × (40 + 30) = 140 lf × 9 ft = 1,260 sqft
- 2. Gables2 × ½ × 30 × 7.5 (rise at 6/12) = 225 sqft
- 3. Openings8×15 + 2×21 + 1×112 = −274 sqft
- 4. Net area1,260 + 225 − 274 = 1,211 sqft = 12.11 squares
- 5. Boxesceil(12.11 × 1.10 ÷ 2) = 7 boxes (14 squares) × $210 = $1,470
- 6. Starter stripceil(140 ÷ 12.5) = 12 pieces = $108
- 7. J-channelceil(259.1 ÷ 12.5) = 21 pieces = $189
- 8. Corner postsceil(4 × 9 ÷ 10) = 4 posts = $128
- 9. House wrapceil(1,485 ÷ 900) = 2 rolls = $270
- 10. Materials subtotal$2,165
- 11. Installed range12.11 × $300–$600 = $3,633–$7,266
The J-channel line is the one nobody prices by eye: 192 lf of opening trim plus 67 lf of gable rakes (30 ft × 1.118 pitch factor, both sides of two gables). It is a tenth of the material bill on this house.
Assumptions & defaults
| Packaging | 1 square = 100 sqft · 2 squares per box of vinyl |
| Opening allowances | Window 15 sqft · door 21 · double garage door 112 |
| Gable geometry | Rise = (width ÷ 2) × pitch/12 · area = ½ × width × rise each |
| Trim lengths | Starter & J-channel 12.5-ft pieces · corner posts 10 ft · wrap 900 sqft/roll |
| Waste (editable) | 10% simple rectangle · 15% cut-up walls, dormers, bays |
| Prices (editable) | Vinyl $105/sq · installed $300–$600/sq · reviewed July 2026 |
The direct-entry mode takes a gross wall area you measured (gables included, openings not deducted) and applies the same opening allowances and packaging math — useful for L-shaped plans, walls of mixed height, or partial re-sides where only some elevations get new siding. The waste rates and why cut-up walls consume more panel are covered in waste factors explained.
The vinyl trim system, piece by piece
| Accessory | Sold as | Counted from |
|---|---|---|
| Starter strip | 12.5-ft pieces | Building perimeter — the level line every course above stands on. |
| Outside corner post | 10-ft lengths | Each outside corner × wall height. Inside corners take a cheaper J-shaped post. |
| J-channel | 12.5-ft pieces | Heads and jambs of every opening, plus both rake edges of each gable. |
| Utility (finish) trim | 12.5-ft pieces | Under window sills and the top course at the eaves — priced inside the J-channel line here. |
| House wrap | 9 × 100 ft rolls (900 sqft) | Gross wall area including gables — the wrap goes on before openings are cut back out. |
Piece lengths and packaging reflect manufacturer installation guides and carton labeling for widely stocked US vinyl products; a specific brand's cartons may vary slightly, so check the label before returning the "extra" box.
How much does new siding cost per square?
Installed vinyl runs $300–$600 per square as an editable national-average range — materials are only about a third of that, which the worked example above shows plainly ($2,165 in materials against $3,633–$7,266 installed). What moves a quote inside the range: tearing off old siding, wall repairs found under it, second-story and steep-lot access, and how much trim detail the elevations carry. The takeoff method behind all of it is on how to estimate materials, and if the siding job is part of a bigger build, the garage cost calculator prices siding as one line of a whole structure.
Sources & standards
Packaging (two squares per box), piece lengths, and trim placement follow the installation manuals published by the vinyl siding trade association and major US manufacturers, and the coverage figures printed on cartons and house-wrap rolls. Opening allowances match the figures used across our wall tools. A water-resistive barrier behind siding is an IRC requirement (section R703) in current code editions — verify specifics with your local building department. Prices reviewed July 2026 — see how our price reviews work.