How to calculate land square metres, decares and hectares
Land area calculation is based on a closed polygon, but CRS, corners, GPS noise and slope affect interpretation.
Field takeaways
- 1 decare is 1000 square metres and 1 hectare is 10000 square metres.
- Area calculation needs a closed polygon and meaningful boundary vertices.
- Phone GPS is useful for approximate work, not official precision.
- Metric area needs suitable CRS handling.
- MapLab Survey keeps area, perimeter, notes and exports together.
The conversions are the easy part
The land conversions everyone uses are simple: one decare is 1,000 square metres, one hectare is 10,000 square metres, one hectare is ten decares. The mistakes almost never come from the arithmetic — they come from the boundary that was measured. The square metres are computed from the polygon you captured, so the number is only as good as its corners, and two careless corners can move the result by several per cent.
How the polygon is built
Take the break points around the land in order and close the polygon. Piling extra points onto a straight boundary does not improve the result — it can add GPS wander instead. Capture the real breaks: corners, turns, ditches, fence bends, boundary changes. And check the closure: an open polygon reports the wrong area, and most software closes it silently between the last and first point.
Step by step
- Open a new project and state the purpose of the measurement.
- Add the parcel or working boundary as a reference layer if one exists.
- Collect the boundary breaks on a polygon layer, or draw them on the map.
- Check the area and perimeter values.
- Document the job with photos, notes and a KML/DXF/CSV export.
Why the registered area can differ
The registered area rests on the official record. The area you walk depends on the occupation line, GPS drift, the data source, transformations and the drawing method. Both numbers can be right at once — interpreting the difference needs the method and coordinate system note beside the result.
Slopes, and which area you mean
Reported map area is the horizontal projection by convention. On sloping ground the surface area is larger — which matters for materials and cultivation, but not for land records. Agree up front which area the job needs, work in square metres, and convert to decares or hectares once at the end so rounding does not accumulate.
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
How is land area calculated?
By calculating the area of a closed boundary polygon.
How many square metres is one decare?
1000 square metres.
Is phone area measurement reliable?
For approximate work, yes. For precision, use controlled survey methods.
Why can deed area differ?
Boundary interpretation, method and CRS can differ.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: Field area calculation · Area measurement app · Registry area comparison · MapLab Survey