Map Area Calculator — Measure Land Area & Acreage
Click on the map or search an address to outline property parcels, farm acreage, or geographical features. Computes enclosed land area in acres, square feet, square meters, and hectares.
Ready to Measure Land Area
Click on the map to place boundary pins or select a sample polygon below to calculate acreage and square mileage.
Click anywhere to add boundary points.True WGS84 Ellipsoidal Surface Area (GeographicLib)
How to use the map area calculator
- 1Outline the area
Click the corners of the field, lot or lake on the map, or search an address to start there.
- 2Compute area on the ellipsoid
The polygon's area and perimeter are calculated on the WGS84 ellipsoid with GeographicLib.
- 3Read acres and hectares
See the area in acres, hectares, square feet and square meters, plus the perimeter.
How to measure area on a map
Measuring property boundaries, lake surfaces, farm fields, or municipal zones requires calculating the area enclosed by an arbitrary polygon. When coordinates are plotted on a 2D computer screen, simple geometry suggests connecting the vertices and computing the polygon area. However, because the surface of the Earth is curved, projecting those points onto a flat plane introduces significant area distortions.
Open Map Lab’s Map Area Calculator calculates geodesic polygon area directly on the surface of the WGS84 ellipsoid. This prevents the substantial exaggeration caused by Web Mercator projections, where high-latitude land parcels can appear up to 400% larger than their actual physical footprint.
How the map area calculator works
Different mathematical methodologies produce radically different results depending on the size of the parcel:
- Cartesian Shoelace Formula (Gauss): Highly effective for small parcels (such as a single suburban lot under 2 acres) where local Earth curvature is negligible. Applying it to regional or continental polygons without projection correction causes massive distortion.
- Spherical Excess (Girard’s Theorem): Evaluates the sum of interior angles of a spherical polygon minus the planar angle sum
(N - 2)π. The excess angle directly relates to the fraction of the globe covered by the polygon. - Karney’s Ellipsoidal Traversal: Implemented by Open Map Lab, this algorithm integrates the area of the geodesic trapezoids bounded by geodesic segments and the equator, ensuring numerically precise area calculations for parcels of any magnitude.
Acres, hectares and square feet explained
Land area units originated in ancient agricultural customs and have evolved into precise legal metrics:
The Acre (43,560 sq ft)
Historically defined as the amount of land a yoke of oxen could plow in a single day (one furlong long by one chain wide: 660 ft × 66 ft = 43,560 sq ft). One square mile contains exactly 640 acres.
The Hectare (10,000 m²)
The international standard unit of land area, defined as a square with 100-meter sides (100 m × 100 m = 10,000 m²). One hectare equals 2.47105 acres.
Example: calculating area on a curved Earth
Demonstration of calculating the spherical excess area of a triangular parcel on a sphere:
E = \alpha + \beta + \gamma - \pi, \quad A = R^2 \cdot E- Planar sum expectation: π = 3.14159265 rad
- Compute spherical excess E: 3.141636 - 3.141593 = 0.00004335 steradians
- Multiply by R²: (6,371,008.8 m)² × 0.00004335 = 1,760,000 m²
- Convert to acres: 1,760,000 / 4,046.86 = 434.90 acres
On small parcels, the angle sum barely exceeds 180°. On continental scales, the excess is huge, demanding exact ellipsoidal trigonometry.
Land area conversion table
Standard conversion factors across international cadastral and real estate frameworks:
Official Land Area Measurement Conversions
Governed by NIST Handbook 44 and ISO 80000-3 standards.
| Unit Name | Symbol | Square Meters | Acre Equivalent | Primary Use Case |
|---|---|---|---|---|
| Square Foot | sq ft / ft² | 0.0929 m² | 0.0000229 ac | Residential home interiors and building footprints |
| Square Meter | sq m / m² | 1.0000 m² | 0.000247 ac | International standard for residential and commercial lots |
| Acre | ac | 4,046.86 m² | 1.000 ac (43,560 sq ft) | US agricultural parcels, real estate listings, zoning |
| Hectare | ha | 10,000 m² | 2.471 ac | Global standard for forestry, agriculture, nature reserves |
| Square Kilometer | km² | 1,000,000 m² | 247.105 ac | Municipalities, metropolitan regions, county areas |
| Square Mile (Section) | sq mi | 2,589,988 m² | 640.0 ac | US Public Land Survey System (PLSS) township sections |
How accurate is a map area measurement?
Before relying on satellite or web-drawn measurements for property boundaries, note the following legal guidelines:
- Not a Legal Survey: Digital map measurements do not substitute for a boundary survey certified by a licensed professional land surveyor (PLS).
- Self-Intersecting Polygons: Polygons with overlapping or twisted edges create mathematical inversion errors in area calculation. Ensure your perimeter outline does not cross itself.
- Elevation & Topography: Map area calculations yield projected planar/ellipsoidal surface area, not the sloped topography of steep hillside acreage.
Explore Related Measurement Tools
Trace custom freehand paths with the Map Drawer Tool or draw exact circular zones using the Map Radius Tool.
Quick facts about the map area calculator
| Fact | Value | Notes |
|---|---|---|
| Mathematical Method | WGS84 Spherical Excess Area | Girard theorem on ellipsoidal facets |
| Supported Units | Acres, Hectares, Sq Ft, Sq Meters, Sq Miles, Km² | Commercial & survey units |
| Perimeter Metric | Boundary Geodesic Length | Sum of perimeter segments |
Edge cases and exceptions
Terrain Slope Area vs. Planar Area
Calculations reflect the horizontal projection on the geoid ellipsoid; steep mountainous terrain has slightly greater 3D surface area.
The map area calculator: worked examples
Commercial Real Estate Land Measurement
Scenario: Tracing the boundary lines of a 4-sided commercial parcel.
Outcome: Computes total area of 4.25 acres (185,130 sq ft) with a perimeter of 1,740 feet.
Frequently asked questions about the map area calculator
How do I measure area on the map?
Click each corner of your property on the map. The tool automatically connects the vertices and calculates the area and perimeter.
How do I measure area on a map?
Click each corner of your shape in order on the map. The tool closes the polygon and reports the area in acres, square feet, square meters and hectares.
How many square feet are in an acre?
43,560 square feet. A square acre is about 208.7 feet on each side.
Is the area calculated on the ellipsoid?
Yes. Area is computed on the WGS84 ellipsoid, not on a flat projection, so large shapes are not distorted by the map.
Can I use this for property boundaries?
It is useful for estimates and planning. Legal acreage comes from a survey, deed or county parcel record.
How accurate is the measured area?
The math is precise; the accuracy depends on where you click. Zoom in and place points carefully on corners.
Does the area include slope?
No. It is the flat (horizontal) area, which is what deeds and parcel maps use. Steep ground has more surface area than shown.
What is a hectare?
A hectare is 10,000 square meters, about 2.47 acres.
Can I measure irregular shapes?
Yes. Add as many vertices as needed. Avoid crossing lines, which make the area ambiguous.
How do I measure a farm field or a lake?
Trace the edge using satellite-like detail, zoom in to follow curves, and add more points for curved edges.
Keep exploring
What to do with this result
- Map Radius Tool — Draw Radius Circles on a MapUse this to draw a radius on a map.
- Map Drawer — Draw Shapes, Polygons & PathsUse this to draw shapes on a map.
- Geographic Center Finder (Centroid & Center of Mass)Use this to find a geographic center.
- Country Size Comparison (True Size of Landmasses)Use this to compare true country sizes.
- GeoJSON Viewer & Map InspectorUse this to view a GeoJSON file.