Calculate area from a KML file with polygon, parcel and field checks
A KML file can be used for area calculation, but reliability depends on source, polygon closure, CRS and field checks.
Field takeaways
- KML usually carries WGS84 latitude longitude data.
- Area calculation needs a closed polygon.
- Google Earth drawing, parcel reference and RTK survey have different accuracy.
- Area results need method notes.
- MapLab Survey helps compare KML with field records.
What the KML actually holds
A KML stores latitude and longitude on WGS84. Area is not stored in the file; it is computed from the geometry when you open it, which is why two applications can report slightly different values for the same polygon. So the honest first question is not "what is the area" but "where did this polygon come from".
Checking it in MapLab Survey
- Add the KML or KMZ to the project as a layer.
- Check that the polygon actually closes.
- Read the area in square metres, decares or hectares.
- Verify the critical corners in the field with photo notes.
- Name the KML source and the method in the report.
Look at the shape before the number
The boundary may have been traced from satellite imagery, exported from old parcel data, or sketched approximately by the client. A polygon drawn on a shifted or three-year-old image inherits that error silently. Open the file and confirm the line sits where it should before trusting anything it produces.
Why projection matters
Computing area directly on latitude and longitude without projecting distorts the result, and the distortion grows with latitude. Use a projected system suited to the region, and note which one you used — the next person to open the file will need it.
Good for planning, not for contracts
A KML area is fine for scouting, comparison and planning. For anything that enters a contract or an official delivery, the starting point has to be a field measurement made with a suitable method; the KML sits beside that measurement, not in place of it.
Try these steps on your own phone.
MapLab Survey handles RTK/GNSS point capture, drawing, area and volume calculations and coordinate conversion, then exports to DXF, KML/KMZ, GeoJSON, Shapefile, GeoPackage, NCZ or CSV. Capture, calculation and export work offline. Live NTRIP corrections and online basemaps need a connection.
Frequently asked questions
Can KML area be calculated?
Yes, if it contains a closed polygon.
Is KML area official?
Not by itself.
Can decare be calculated from KML?
Yes, from square metres.
Can MapLab Survey check KML in the field?
Yes.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: Open KML file · Polygon drawing app · Decare calculator · MapLab Survey