Click around a field, a building or a lake to draw its outline and read the area in every unit, with the perimeter and the centre. Several shapes add up. Or paste the corner coordinates.
How to use it
Zoom the map to the place. Press Draw a shape.
Click each corner of the area. Double-click, press Enter, or click the first corner again to close the shape.
Draw more shapes to add them up. Undo removes the last shape.
Read the area in every unit, the perimeter and the centre. Download the shapes as GeoJSON.
5 practical uses
Measure a field, a paddock or a garden for seed, fertiliser or turf.
Measure a roof for solar panels or a car park for marking.
Check the area of a plot of land against the deed.
Measure a lake, a wood or a burnt area for a report.
Estimate the paint, gravel or tarmac a surface needs.
The maths behind it
The area is the geodesic area on the WGS84 ellipsoid, computed with the method of Chamberlain and Duquette: for each edge, (λ₂ − λ₁)·(2 + sin φ₁ + sin φ₂) is summed and scaled by R²/2, which gives the signed area of the polygon on the sphere. The perimeter is the sum of the haversine lengths of the edges; the centroid is the area-weighted centre of the planar polygon.
As the geodesic area on the WGS84 ellipsoid, so it is correct at any latitude and for any size, unlike an area measured on the flat map.
Can I paste coordinates instead of drawing?
Yes. Paste one corner per line as latitude, longitude and press Add pasted shape.
How many corners can a shape have?
As many as you click. For a field or a plot, ten to twenty corners is usually enough for the area to be within a percent.
Embed this tool on your website
Paste this code where the tool should appear. It shows the tool alone, without this page's text, and links back here. It is free to use; the map data credit stays on the map.
Change height to suit your page. To open the tool with a place already set, add the settings from this page's address bar (the part after #) to the end of the src. The embedded tool asks the visitor's browser for their location only when they press the button, and the allow attribute lets that work inside the frame.