How to use the map calculator
- Find your land. Zoom and pan the map, or press Use my location if you are standing on it. Zoom in as far as you can — corners placed at close zoom are far more precise.
- Place the corners in order. Click or tap each corner, going around the boundary in one direction. The shape closes itself; there’s no need to click the first point again.
- Adjust. Drag a point to move it. Select a point and press Delete point to remove it, or use Undo.
- Read the result. The area appears in acres, hectares, square meters, square feet, square yards, square kilometers and square miles, with the perimeter in meters, kilometers, feet, yards and miles.
Switch to Distance to measure a path, a fence line or the length of a road frontage instead. The page address keeps your points, so you can bookmark the page or send the link to someone.
Walking the corners with your phone
On a phone you can collect the corners on foot. Press Use my location and allow location access, walk to a corner, stand still for a few seconds while the accuracy figure settles, then press Add point here. Phone GPS is typically good to a few meters under open sky and worse under trees or next to buildings, so check each point on the map before moving on. Our guide to phone GPS accuracy explains what to expect.
How the area is calculated
Corners on a map are latitude/longitude pairs on a curved Earth, so the calculator doesn’t treat them as flat x/y points. It splits the polygon into triangles that share the first corner and adds up their spherical excess — the amount by which each triangle’s angles exceed 180° — on a sphere with radius R = 6,371,000 m. Multiplying the total excess by R² gives the area in square meters. This handles concave plots and shapes that cross the 180° meridian, and it is the same formula, line for line, as the Land Measure app, so the website and the app give the same numbers for the same corners.
The perimeter adds the great-circle (haversine) distance of every side, including the closing side back to the first corner. Units are converted with the exact international definitions: 1 acre = 4,046.8564224 m² (43,560 ft²), 1 hectare = 10,000 m², 1 ft = 0.3048 m.
Worked example
A rectangular field near Ames, Iowa with these four corners:
| Corner | Latitude | Longitude |
|---|---|---|
| 1 | 41.88000 | −93.62000 |
| 2 | 41.88000 | −93.61400 |
| 3 | 41.87550 | −93.61400 |
| 4 | 41.87550 | −93.62000 |
The east–west sides are about 496.7 m and the north–south sides about 500.4 m. The calculator gives an area of 248,565 m², which is 24.86 ha or 61.42 acres, and a perimeter of 1,994.26 m (6,542.9 ft). Open this example on the map.
Limits worth knowing
- Sphere vs. ellipsoid. The Earth is slightly flattened. A spherical model differs from an ellipsoidal (WGS 84) calculation by a fraction of a percent, depending on latitude — fine for planning, pricing and fencing, but not a substitute for a survey.
- Map vs. legal boundary. Fences, hedges and field edges on a map are not always where the legal boundary is. For deeds, disputes or permits, ask a licensed surveyor.
- Holes. A shape here has one outer boundary. To exclude a pond or building, measure it separately and subtract.