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GeoJason

GeoJSON Area Calculator

Calculate the area of GeoJSON polygons in square meters and square kilometers.

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Turf measures area on the WGS 84 ellipsoid, so the number is a real ground measurement. Treating longitude and latitude as a flat grid gives square degrees, and the difference is large: a degree of longitude is about 111 km at the equator and near zero at the poles.

Results come back in square metres, hectares, square kilometres, square miles and acres. Paste a FeatureCollection with more than one polygon and you also get a per-feature table, labelled from each feature's name, title or id. Only polygons enclose an area, so points and lines contribute zero.

How Area Calculation Works

This tool calculates the geodesic area of Polygon and MultiPolygon features in your GeoJSON data. It uses the WGS 84 ellipsoid model for accurate results regardless of where on Earth the polygon is located. The area is reported in square meters, hectares, square kilometers, square miles, and acres.

If your GeoJSON contains multiple polygons in a FeatureCollection, the tool reports the combined total and a per-feature table beneath it, labelled from each feature's name, title or id property and falling back to its position in the file. Non-polygon geometries are ignored since they have no area. Polygons with holes are handled correctly: the hole area is subtracted from the outer ring.

Understanding Area Units

  • Square meters (m²): standard metric unit, useful for parcels and buildings
  • Square kilometers (km²): useful for cities, counties, and regions
  • Square miles (mi²): common in the United States for land area
  • Hectares, the usual unit for farmland outside the United States (1 ha = 10,000 m²)
  • Acres, widely used in real estate and agriculture (1 acre is about 4,047 m²)

As a reference, Manhattan is approximately 59 km² (23 mi²). A standard American football field including end zones is about 5,350 m². Central Park is roughly 3.4 km². These benchmarks help you sanity-check your results: if a city block comes back as 50 km², something is wrong with the input data.

Geodesic vs. Planar Area

This tool uses geodesic area calculation, which accounts for the curvature of the Earth. Planar area calculations that treat latitude and longitude as flat coordinates produce increasingly wrong results for larger polygons and for polygons near the poles. The overestimate is roughly one divided by the cosine of the latitude: about 1.4 times at 45°N and about 2 times at 60°N.

For small polygons near the equator, the difference is negligible. For anything larger than a city block, geodesic calculation is strongly recommended, and that is what this tool always uses.

What Area Figures Get Used For

  • Calculating property or parcel sizes from boundary data
  • Measuring the coverage area of service zones or delivery regions
  • Estimating land use from zoning polygons
  • Verifying area calculations from GIS software exports
  • Computing forest, wetland, or agricultural coverage from satellite-derived polygons
  • Comparing polygon areas before and after simplification

Computing Area Without This Page

In JavaScript with Turf.js:

JavaScriptconst areaM2 = turf.area(polygon);
const areaKm2 = areaM2 / 1_000_000;

In Python with Shapely and pyproj:

Pythonfrom shapely.geometry import shape
from pyproj import Geod
geod = Geod(ellps="WGS84")
polygon = shape(geojson_geometry)
area_m2 = abs(geod.geometry_area_perimeter(polygon)[0])

For measuring distances instead of areas, use the length calculator. To find the geographic center of a polygon, try the centroid calculator.