How do you measure a house for siding?

Per elevation: width × height, minus large openings (garage doors), plus gables as half-base-times-height. Sum to squares (100 sq ft). Small windows usually stay in the number — the cutting and trimming around them costs what the hole saves.

What waste factor for siding?

10% for simple boxes, 12–15% for cut-up elevations with many gables and dormers. Diagonal-cut products and staggered-seam patterns run higher.

What do siding estimates miss most?

Layers under the existing siding, rotten sheathing, and trim linear footage. Tear-off surprises and uncounted J-channel are the classic margin killers.

Field guide

How to Estimate a Siding Job Without Getting Burned by the Wall

Two identical-looking houses can be a full day apart in labor once the first course comes off. Estimating siding is estimating what you can't see yet — so the method is measure precisely, grade what's visible, and structure the unknowns as allowances with unit prices.

Step 1 — Squares per elevation

Measure each elevation: width × height to the eave, gables as ½ × base × height. Subtract garage doors and picture windows; leave normal windows in — the trim labor around them eats the area they save. Keep elevations as separate lines: access differs, condition differs, and "what if we skip the detached garage" becomes a one-line answer.

Step 2 — Find out what's on the wall now

Pull the corner of a course or check at the meter: how many layers, and what's under them? One layer of vinyl over wrap is a clean day. Wood over fiberboard over original clapboard is demolition. Price tear-off per square by what's actually there, plus a dumpster count that matches.

Step 3 — The sheathing allowance

Somewhere behind that wall is soft OSB — at a downspout, below a window, behind the planter. Carry a named allowance (e.g., four sheets included) plus a per-sheet unit price for more. This single line converts the job's biggest unknown into a signed change order instead of a standoff.

Step 4 — Count trim like it's the job (it is)

Corners, inside and outside, by piece and height
J-channel and starter by linear foot
Window/door trim per opening — count the openings on every elevation
Fascia and soffit by linear foot, vented vs. solid noted
Shutters off and on, light blocks, dryer vents, spigot rings

Step 5 — Access, then margin

Note stories per elevation, grade drops, decks you'll stage over, and anything needing pump jacks or a lift. Then total direct cost, apply overhead, and divide by (1 − target margin) — the divide method, not cost × margin. Check the difference on your own numbers with the free margin calculator.

Step 6 — Send it the same visit

FieldSquire turns the narrated walk — squares, layers, the soft spot photo, the opening count — into editable lines at your saved rates and sends a branded, signable PDF from the driveway. See the siding estimating app workflow free for 14 days.

Try it on a real job: FieldSquire's Solo plan is free for 14 days with no credit card — unlimited manual estimates and AI-assisted drafts you review line by line. Start the free trial or see the siding estimating app guide.