GeoJason

GeoJSON Area Calculator

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

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Area on a sphere is not the area you'd compute on a flat plane. A polygon drawn at the equator and the same polygon drawn near the pole have very different surface areas in square metres, even though their corner coordinates span the same number of degrees. Tools that just multiply width by height get this wrong, sometimes by 30% at high latitudes.

Paste a Polygon, MultiPolygon, or FeatureCollection containing them and the tool reports the area in square metres, hectares, and square kilometres, plus a per-feature breakdown if you've passed multiple polygons. The math is geodesic — it accounts for Earth's curvature using the spherical-excess formula, the same calculation PostGIS's ST_Area(geography) performs.

Below the calculator you'll find the formula it uses, a comparison with the planar ST_Area(geometry) result (which is in square degrees and almost never what you want), and the Turf.js / Shapely equivalents for scripted use. For polygon hygiene before measuring, run the validator first — unclosed rings produce wrong areas silently.

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, square kilometers, square miles, and acres.

If your GeoJSON contains multiple polygons in a FeatureCollection, the tool reports the total combined area across all polygon features. Non-polygon geometries (Points, LineStrings) are ignored since they have no area. Polygons with holes (interior rings) are handled correctly — the hole area is subtracted from the outer ring area.

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
  • Acres — widely used in real estate and agriculture (1 acre ≈ 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. A polygon at 60°N latitude would have its area overestimated by roughly 4x with planar math compared to true geodesic measurement.

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.

Common Use Cases

  • 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

Programmatic Equivalent

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.