Area & Perimeter Calculator

Why area from lat/long is not simple arithmetic

A degree of longitude is about 111 km at the equator and zero at the poles, so you cannot treat latitude and longitude as a flat grid and multiply. Doing so overestimates area near the equator and badly underestimates it at high latitudes. This tool computes the area on the sphere directly using a spherical excess formula, which gives results within a fraction of a percent of what PostGIS ST_Area(geography) reports — accurate enough for parcels, zones and site plans.

What gets measured for each geometry type

Polygons and MultiPolygons return an area; their outer ring counts positive and every inner ring (a hole) is subtracted, so a doughnut-shaped parcel reports its true footprint. Perimeter is the great-circle length around every ring. LineStrings return length only. Points contribute nothing, which is why a point-only dataset shows a total area of zero rather than an error.

• Polygon → area plus perimeter, holes subtracted
• MultiPolygon → sum of all parts
• LineString / MultiLineString → geodesic length
• Point / MultiPoint → no measurement

Choosing units for real work

Square metres are right for buildings and individual plots. Square kilometres suit districts, catchments and administrative boundaries. Acres remain the working unit for land transactions in much of the world, and in South Asia you will often need to convert onward to bigha or katha — the acre figure here is the correct starting point for that. All three are shown at once so you do not have to convert by hand.

How much to trust the number

The measurement is only as good as the geometry. A polygon digitised from a low-zoom satellite image can easily be several percent off, and simplified boundaries lose area at every removed vertex. If the figure matters legally, treat this as a check on a surveyed number rather than a replacement for one — and validate the file first, because unclosed rings and swapped axes produce confident, wrong answers.