County Maps US

Tools Distance, area and drive time

Map Area Calculator

Click to place corners, close the shape, and the area and perimeter are computed from the corner coordinates on the globe, so a field in Alaska measures as accurately as one in Texas.

How to use it

  1. Zoom the map to the land you want to measure, or type a place to jump there.
  2. Click each corner in order around the outline. Drag a marker to correct it; Undo removes the last corner.
  3. Press Close shape when the outline is complete. The area and perimeter update as you work.
  4. Enter a price per acre or per hectare to get a total, and export the outline as GeoJSON or KML.

How it works

Corners are stored as latitude and longitude, and the area is the spherical polygon area of that ring on a sphere of radius 6,371 km, computed in the browser. The perimeter is the sum of the great-circle edges. Neither depends on the map projection or the zoom level, so the figures do not change when you pan or zoom.

Accuracy is limited by where you click: at zoom 16 a pixel is about 2 metres, so trace parcel corners at zoom 17 or above. The tool does not read parcel boundaries; it measures what you draw. Spherical rather than ellipsoidal area understates by at most about 0.3 percent.

Questions

How do I measure acreage on a map?
Click around the boundary of the land, press Close shape, and read the Acres row. For a farm, zoom in far enough to see the fence lines or field edges before clicking.
How accurate is the area?
The calculation is exact for the corners you place. The uncertainty comes from your clicks, so for a one acre lot zoom in until the lot fills the screen. Land records from the county assessor remain the legal figure.
Can I move a corner after placing it?
Yes. Every corner is a draggable marker. Drag it to the new spot and the area updates when you let go.
What does cost per unit do?
It multiplies the measured area by the price you type, in the unit you pick: price per acre, per hectare, per square foot and so on, for a quick land value or seeding estimate.

All map tools, free and without an account. Location data is processed in your browser and by the open geocoding services named on the sources page; nothing is stored by this site.