House Washing Square Footage Calculator

Perimeter × wall height, plus the gables. Walk the outside of the house and add up the wall runs to get the perimeter — for a simple rectangular house that's 2 × (length + width). Multiply by the total wall height, which is the number of stories times roughly 9 feet per story. Then add each gable end as a triangle: ½ × width × rise. A 40 × 28 ft two-story with two medium gables works out to 136 ft of perimeter × 18 ft of wall = 2,448 sq ft, plus 168 sq ft of gable, for 2,616 sq ft of washable siding.

Because living area and siding area are two different surfaces that happen to land in a similar range by coincidence. Across the six common house sizes in the table on this page, siding area runs anywhere from 0.95× to 1.33× the listed living area — a spread wide enough to cost you a few hundred dollars on a single quote. A 1,800 sq ft two-story has about 2,400 sq ft of siding; a 3,600 sq ft two-story has about 3,420. Use the listing figure as a sanity check on a number you calculated, never as the number itself.

No, and confusing the two is the most expensive mistake on a house wash. The footprint is the flat area the house covers — what a length × width calculator gives you. Siding is the vertical surface wrapping the outside of it. On a typical two-story the siding is about 2.3× the footprint, so quoting off the footprint means bidding roughly a third of the job. The footprint is still worth knowing as a cross-check, because for a rectangular house it should equal length × width from the same two numbers you used to get the perimeter.

Usually not. You are washing the glass, the frames, the trim and the sills anyway — often more carefully than the flat siding around them — so the time doesn't come off the job just because the surface changes material. Most contractors quote gross wall area and let the openings ride. The exception is a wall that's mostly glass, like a sunroom or a wall of sliders, where deducting is defensible because you genuinely aren't soft washing 200 sq ft of siding that isn't there.

Residential house washing commonly runs $0.15 to $0.30 per square foot of siding, which puts a single-story ranch around $250–$400 and a two-story around $450–$700 before add-ons. Those are market ranges, not your price. Your number should come from your own production rate and overhead: if you wash 2,600 sq ft in three hours and you need $150 an hour on the truck, that job is $450 and the per-foot rate is an output of that math, not an input to it.

Siding absorbs roughly one gallon of mixed solution per 250 square feet, so a 2,600 sq ft house takes about 10 gallons of mix. Rough or heavily textured surfaces — stucco, older wood, dry brick — pull toward 200 sq ft per gallon, and smooth vinyl stretches toward 300. Once you know the gallons, the soft wash mix calculator turns that into the sodium hypochlorite and water split at whatever strength you're targeting.

No. Every input is taken from the ground. The perimeter is a walk around the outside of the house, the wall height comes from counting stories rather than measuring them, and gables are estimated from their width and rise using standard sizes. Nothing about a house wash measurement requires you to leave the ground, which is exactly why it can be done on the first visit — or from the driveway while you're measuring the flatwork.

No — satellite imagery is an overhead view, so it sees the roof and the footprint, not the walls. SurfaceMeasure measures flat surfaces: driveways, walkways, patios, pool decks, and parking lots. That still matters on a house wash, because the house is almost never sold alone. Use the calculator on this page for the siding, then trace the flatwork on the same property from satellite and put both on one quote.

SurfaceMeasure starts with 1 free measurement — no credit card required. Paid plans are $9.99 per month or $99.99 per year. The calculator on this page is free and always will be; you don't need an account to use it.