Measure a property from satellite, free

There are four tabs, and each one says where its number comes from before you use it.

• Roof. Type the address. Koira asks Google's Solar API for the building at that spot. Google keeps a 3D model of millions of roofs, built from aerial and satellite pictures, and splits each roof into planes. For every plane it gives the area with the tilt already in, the pitch in degrees and the direction it faces. Koira adds the planes up, turns the total into roofing squares, and works out how many bundles to order with your waste allowance.
• Lawn and lot. Type the address. Koira reads the lot size off the county property roll for the parcel at that spot, in the counties and states it reads (about 40 records, including statewide rolls for Florida, New York, New Jersey, Maryland, Connecticut and Wisconsin). For the yard, it takes out the house footprint (the living area over the stories) and a tenth for the drive and walks.
• Draw area. Open the satellite map and tap the corners of anything flat: a lawn, a driveway, a lot, a roof from above. Add as many areas as you like. Use Cut out to take away the house, a pool or a patio. You get square feet, square yards, acres and the distance around.
• Draw line. Tap along a fence line, a run of gutter or a bed edge. Each run adds to the total in feet.

Under every answer, "How we got this" lists each step with its numbers, so you can check the work or explain it to a customer.

It depends on the picture and on the method. Here is what each one rests on.

Each answer carries a confidence line in plain words. For a roof, it is Google's own quality grade and the month the picture was taken. If the model found only one plane on a house, the tool says that is unusual and asks you to check it on the map.

A roofing square is 100 sq ft of roof. Standard strip and laminate shingles come three bundles to a square. So the order is the roof area divided by 100, times 3, plus the waste you expect, rounded up to a whole bundle.

Take a roof that measures 2,000 sq ft. That is 20 squares. At 10% waste: 20 × 3 × 1.10 = 66 bundles. At 15% waste: 20 × 3 × 1.15 = 69 bundles.

IKO puts shingle waste at about 10 to 15 percent. Simple gables with few cuts sit at the low end. Hips, valleys and dormers mean more cut pieces and push it toward 15. Pick your waste on the Roof tab and the bundles change as you tap.

Heavier designer shingles can come four or five bundles to a square. Check the wrapper for the coverage of the line you are buying and adjust.

A satellite picture looks straight down, so a roof you draw on the map is its footprint, not its surface. A steeper roof has more surface over the same footprint. Google's model already includes the tilt in each plane's area, so the Roof tab needs no multiplier. When you draw a roof yourself, pick its pitch under the map and the tool multiplies the footprint for you.

The multiplier is plain geometry: √(1 + (rise ÷ 12)²), the length of a rafter over the length of its run. The angle is the arctangent of rise ÷ 12.

If you do not know the pitch, the Roof tab's answer names the pitch that covers the most of the roof, in the x/12 roofers use and in degrees.

For lawn care, fertilizer and seed, what you need is the turf, not the lot. The Lawn and lot tab starts from the county's lot size and works toward the yard:

• Lot size from the county roll. Lots recorded in acres are turned into square feet at 43,560 sq ft an acre.
• House footprint: the living area on the roll divided by the number of stories.
• Yard: the lot less the footprint, then less a tenth for the drive, walks and patio.

A quarter-acre lot is 10,890 sq ft. With a 2,400 sq ft two-story house, the footprint is 1,200 sq ft. The yard is (10,890 − 1,200) × 0.9 = 8,721 sq ft.

That is a good first number for a phone quote. For the real one, switch to Draw area, trace the lawn and cut out the beds, the pool and the patio.

Every answer has "Use in a calculator" buttons that open a price tool with the measurement already filled in:

• Roof area and pitch go to the roof replacement cost calculator.
• Lawn square feet go to the lawn care cost calculator.
• Fence feet go to the fence cost calculator, and gutter runs to the gutter cost calculator.
• Drive and patio square feet go to the pressure washing cost calculator.

Print gives you a clean sheet with the numbers and the steps. "Save to a Koira estimate" opens a free Koira office, where the measurement goes on an estimate you send from your phone. Inside Koira, the same measuring sits on every estimate: tap "Measure it on the map" and the square feet land on the line. See how estimates work in Koira.

Paid measuring sells things this tool does not do. Hover sells exterior measurements from a scan of the house, EagleView sells walls, windows and doors reports, and QuoteIQ puts map measuring and automatic tracing inside its paid plans. Ridge, hip and valley lengths need the lines where the roof planes meet, and Google's Solar model does not give those lines, so this tool does not show them rather than guess.

What this tool gives for free: the roof area, pitch and planes from Google's model, the lot from the county roll, and drawing tools for any area or line. For a side by side with dated prices, see the free Hover alternative page.