How to Measure Siding: Square Footage & Siding Squares

Siding is measured by wall area, not floor area, and the method is the same for every material: take the perimeter of the house, multiply by the wall height, add the gable triangles, subtract the windows and doors, then divide by 100 to get siding squares (1 square = 100 sq ft). Add a 10–15% waste factor and that's what you order. For our typical two-story house that comes to about 2,775 sq ft, or 28 squares net — here's the full method, worked end to end.

The 30-second method

Everything reduces to one formula:

(Perimeter × wall height) + gable triangles − openings = siding area

Then siding area ÷ 100 = squares, and squares × (1 + waste %) = what you order. A "square" is just the trade's word for 100 sq ft of coverage — it's the unit siding is boxed, ordered, and often quoted in (Inch Calculator). The only judgment calls are how you handle openings and how much waste to add, and those two choices are exactly why two honest contractors can hand you different numbers.

Step by step: measuring our typical two-story

Take our standard project — a ~2,000 sq ft two-story house on a 45×30 ft footprint, 19-ft walls, a gable roof, and 12 windows, 2 doors, and 1 (double) garage door. Work it in order:

Component	Formula	Result
Perimeter	2 × (45 ft + 30 ft)	150 ft
Rectangular wall area	150 ft × 19 ft	2,850 sq ft
Two gable triangles	2 × (30 ft × 7.5 ft ÷ 2)	225 sq ft
Gross wall area	2,850 + 225	3,075 sq ft
Openings deducted	12 windows + 2 doors + garage	−300 sq ft
Net siding area	3,075 − 300	2,775 sq ft
In squares	2,775 ÷ 100	~28 squares

A few notes on the rows:

• Perimeter × height is the bulk of the job. For a two-story, the 19-ft height already bakes in both floors, so you don't measure each story separately.
• Gable triangles use base × height ÷ 2. Our gable ends are 30 ft wide; at a moderate roof pitch the peak rises about 7.5 ft, so each triangle is (30 × 7.5) ÷ 2 = 112.5 sq ft (Today's Homeowner). A hip roof has no gables; a home with dormers has extra little ones.
• Openings here are 12 windows × 12 sq ft (144) + 2 doors × 21 sq ft (42) + one double garage door at 16×7 ft (112) ≈ 300 sq ft. Deduct the full area of each opening.

Convert to squares — and why floor area lies

Divide the net area by 100 and you have squares: 2,775 ÷ 100 ≈ 28 squares. That's the number a supplier wants, because siding ships and prices by the square.

Notice the trap in the phrase "2,000 sq ft house." That's floor area. Our two-story carries 2,775 sq ft of actual siding — nearly 40% more than its floor plan — because both stories and the gables are wall. This gap is why online "cost to side a 2,000 sq ft house" figures scatter so widely: a single-story ranch and a two-story colonial can share a floor area yet need very different amounts of siding.

Add the waste factor

You never order the exact net area. Every cut around a window, corner, or gable end leaves an off-cut you can't always reuse, so you pad the order. The factor depends on the material and the house:

Siding type	Typical waste factor
Vinyl lap	10% (7–10%)
Engineered wood lap	10–12%
Fiber-cement lap	12%
Wood shakes / shingles	15%
Complex home (many corners, gables, dormers)	up to 20%

For our house in vinyl, add 10%: 2,775 × 1.10 ≈ 3,050 sq ft, so order 31 squares (Today's Homeowner). In fiber cement at 12% it's ~3,110 sq ft. The waste isn't lost money you'll never see — it covers real cuts, breakage, and the offcuts that keep a job moving, plus a little attic stock for future repairs.

Why contractor measurements differ

If you collect three bids, the square footage on each may not match. That's usually not a mistake — it's method:

• Gross vs. net. Some estimators price the full wall area and never deduct openings, treating the windows and doors as free waste buffer. Others net every opening out. On our house that's a ~300 sq ft (3-square) swing.
• Small-opening treatment. A common shortcut is to deduct only large openings (garage, patio doors) and leave small windows in. Faster, and it self-insures against under-ordering.
• Gable and dormer estimating. Triangles and dormers get eyeballed or rounded differently from one estimator to the next.
• Waste percentage. One bid at 10% and another at 18% can differ by two full squares on the same measured wall.

The fix when comparing bids: ask what wall area each quote is based on, not just the dollar total. Same area, different price is a real comparison; different area is two different scopes.

From squares to cost

Multiply your net wall area by our installed per-square-foot rates (materials + labor) to turn the takeoff into a budget:

Material	Installed $/sq ft (typ)	~2,775 sq ft
Vinyl	$7	~$19,400
Fiber cement	$9	~$25,000
Engineered wood	$10	~$27,800
Wood	$12	~$33,300

Those installed figures line up with 2026 market ranges — fiber cement runs about $5–$14/sq ft installed, vinyl on the lower end (This Old House). Two line items ride on top of the same wall area: tear-off at $0.75–$2/sq ft (about $2,100–$5,500 here) if old siding has to come off first, and a permit at $100–$400. The full pricing breakdown is in how much does siding cost, and the material trade-off is in vinyl vs. fiber cement.

Get your number

The calculator does this whole takeoff for you: enter your perimeter, wall height, gable count, and openings, pick a material and waste factor, and it returns the siding area, the squares to order, and the installed low/mid/high cost — with the math shown, so you can check it against any contractor's measurement. See the siding hub for the rest of the guides.

Open the siding cost calculator →