Map Area Calculator
Click three or more points on the map to outline any land parcel, park, neighborhood, or region and compute its spherical surface area in acres, square miles, square kilometers, hectares, and square feet.
Click anywhere on the map below to place vertices (at least 3 points for area), or load a sample polygon above.
Polygon Area, Perimeter & Vertices
Radius map tool Distance between cities Crow-flies distance Latitude & longitude finder
How Map Polygon Surface Area Is Calculated on a Sphere
This map area calculator measures the true surface area and perimeter of any closed polygon drawn on the globe by applying the 3D spherical excess (solid-angle) formula on the International Union of Geodesy and Geophysics (IUGG) mean Earth sphere (R = 6,371,008.8 meters), rather than measuring flat projected pixels on a Web Mercator canvas. As soon as you place three or more vertices on the map, the tool converts your polygon into a closed ring, triangulates the spherical solid angle from the first vertex using the Van Oosterom & Strackee vector formula, and outputs the area across five standard units simultaneously:
- Acres (U.S. / International): Exact conversion at
1 acre = 4,046.8564224 square meters(43,560 square feet), the primary unit for U.S. real estate parcels, farms, ranches, and parks. - Square Miles & Square Kilometers: Ideal for municipal boundaries, watersheds, wildfire perimeters, and regional planning (
1 sq mi = 640 acres = 2.589988 sq km). - Hectares & Square Feet: Metric land measurement (
1 hectare = 10,000 m² ≈ 2.47105 acres) and square footage for smaller lots, roofs, and athletic fields.
Why Spherical Excess Beats Flat Map Projection Math
A standard Web Mercator map stretches surface area by a factor of 1 / cos²(latitude). At 40°N latitude (such as Denver, Philadelphia, or Columbus), a naïve pixel-area calculation overestimates land area by 70%; at 61°N in Anchorage, Alaska, it overestimates area by more than 325%. Because QuickWhere computes solid angles directly from 3D unit vectors on the sphere and sums great-circle edge lengths for the perimeter, a 1-acre lot in Florida and a 1-acre lot in Alaska both measure accurately without projection distortion.
Tips for Drawing Accurate Polygons
Place vertices in sequential order (clockwise or counter-clockwise) around the perimeter of your property or region, and avoid crossing polygon edges over one another (self-intersecting figure-eight shapes subtract opposing loop areas). Use Undo Last Point if you misclick, or switch to the Radius Map Tool to measure circular areas.