Siding Calculator

What this siding calculator does

This calculator works out how much exterior siding you need to cover a house — in square feet, squares (the trade unit, 100 sqft each), and the linear feet of J-channel and starter strip that almost every estimate forgets. It subtracts standard 15 sqft windows and 21 sqft doors automatically, multiplies for one, two, or three stories, and applies a 10 % waste factor by default. All math runs on your device — your house measurements never leave the page.

How to use the siding calculator

1. Pick a measurement mode. If you’ve walked around with a tape and a clipboard you’ll know the perimeter already. If you only have a rectangular footprint, use L × W.
2. Enter wall height per story (9 ft is the modern US standard; 1950s homes are often 8 ft; some new builds run 10 ft on the first floor).
3. Pick the number of stories. The calculator multiplies wall area accordingly.
4. Enter the count of standard windows and doors. The calculator subtracts 15 sqft per window and 21 sqft per door — these are national averages; small bathroom windows or oversized patio doors should be counted in proportion.
5. Adjust the waste slider. 10 % is the industry default; bump higher for homes with many gables, dormers, or angled walls.
6. Read squares for ordering, and don’t skip the trim & accessories card — J-channel and starter strip are where most amateur estimates fall short.

Why “squares”?

The square as a unit of siding goes back to early American carpentry, when framing was laid out in 10 ft × 10 ft bays — one bay being one “square” of wall to clad. The number stuck even as homes got larger: vinyl manufacturers still ship cartons of two squares (200 sqft); fibre-cement plank is still listed per square in pricing sheets; roofing follows exactly the same convention. When a contractor quotes you “$1,200 per square installed”, that’s $12 per sqft of finished siding — and a 2,000 sqft wall would come in at around $24,000 installed.

Material choices in 2026

Three major materials dominate the US residential siding market:

Vinyl siding is the most common, installed on roughly two-thirds of new US homes built in the last twenty years. Cost runs $4–8 per sqft installed; lifespan 20–40 years; maintenance-free — it never needs paint and rinses clean with a garden hose. Drawbacks: fades over decades, can crack in extreme cold, and looks unmistakably plastic up close.

Fibre cement siding (James Hardie HardiePlank is the dominant brand) is the premium choice. Cost $7–13 per sqft installed; lifespan 30–50 years; needs a paint refresh every 10–15 years. It looks closest to traditional painted wood and stands up to fire, termites, and salt air better than any other option. The drawback is weight — about 2.5 lb per sqft versus 0.5 lb for vinyl — which makes installation slower and labour costs higher.

Engineered wood siding (LP SmartSide is the dominant brand) splits the difference. Cost $6–11 per sqft installed; lifespan 20–30 years with proper maintenance; can be painted or factory- finished. It’s lighter and faster to install than fibre cement, but needs more attentive caulking and repaint cycles.

What the calculator can’t see

Three real-world adders the math can’t infer from a perimeter:

Gables and dormers add wall area above the main wall height. A typical front gable on a single-story ranch adds roughly 60–120 sqft depending on roof pitch. The calculator does not account for gables — add the gable area manually to your perimeter calculation if your house has them.

Soffits and fascia are usually sided in a different material (aluminium or vinyl soffit panels with vented inserts). They’re not included in this calculator. A typical 2,000 sqft single-story home needs about 200 sqft of soffit and 160 linear ft of fascia.

Trim, corners, and J-channel are accessory items that are sold separately from the main siding. The calculator estimates J-channel (perimeter plus 4 linear ft per opening) and starter strip (perimeter) — both at standard rates. For inside / outside corner posts, allow one piece per corner and order in 10 ft lengths.

Why 10 % waste

Siding waste is real and consistent:

• Cut-off ends. A board that doesn’t reach the end of a wall has to be cut. The off-cut might or might not be long enough to start the next course.
• Pattern matching. Wood-grain or shadow patterns must be matched across joints; mismatched pieces become waste.
• Damage. A bottom-of-pallet piece chips on the way out of the truck. A wall piece is gouged by the laser level. 1–2 % over the full job.

10 % covers all of it for a typical rectangular two-story home. Bump to 12–15 % for cape-cod, victorian, or any home with multiple gables, dormers, or angles — every angle creates two new cut-edges.

Privacy

This calculator does its arithmetic in JavaScript on your device. There is no fetch call, no analytics on the values you enter, no server-side logging. The page works the same way offline once loaded.