Measure area on a map
Area
101.58 ha
Perimeter 4.032 km (2.505 mi)
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Up to 500 rows. Read in your browser, never uploaded.
One corner per row: name (optional), latitude, longitude. Decimals use a point. Addresses are not looked up.
Every unit, and share
- 101.58 ha
- 251 ac
- 1.016 km²
- 0.3922 mi²
- 1,015,771.5 m²
- 10,933,673.4 ft²
Perimeter: 4,032 m = 13,227 ft.
WGS 84 · geodesic · Guide, examples and sources below
How do I measure the area of a field or a lot on a map?
Click the corners of a shape on the map, three or more, and the area and the perimeter appear. Switch between hectares, acres, square kilometers and square miles.
Click the corners of the shape one after another, going around it in either direction. From the third click on, the tool closes the polygon for you and shows the area and the perimeter. Zoom in before you click along a curved edge so the corners follow it closely; more corners mean a better fit. Use Undo to remove the last corner or Clear to start again.
The unit buttons switch between hectares, acres, square kilometers and square miles, and the details list also gives square meters and square feet. The perimeter includes the closing edge from the last corner back to the first. If you already have the corners as coordinates, type them one at a time into the box, which takes decimal degrees, degrees-minutes-seconds and UTM, or load the whole list at once from a CSV file in the panel, one corner per row.
What exactly is being measured?
The area is the size of the shape on the WGS 84 ellipsoid, the mathematical Earth used by GPS. The edges are geodesics, the shortest paths between corners, and the area is computed with Karney’s method for geodesic polygons. It is the area of the shape projected onto that smooth surface, not the area of the terrain: a steep hillside has more ground than the map area shows.
Worked example. Starting at 47.6000, -122.3000, a square built 1,000 m east, 1,000 m north and back measures 0.9999 km², which is 99.99 hectares or 247.08 acres, with a perimeter of 3,999.83 m. The sides are geodesics on a curved surface, so the figure is very close to 1 km² but not a perfect square.
How do hectares, acres and square kilometers compare?
| Unit | In square meters | In hectares | In acres |
|---|---|---|---|
| Hectares | 10,000 m² | 1 ha | 2.471054 ac |
| Acres | 4,046.8564224 m² | 0.404686 ha | 1 ac |
| Square kilometers | 1,000,000 m² | 100 ha | 247.105381 ac |
| Square miles | 2,589,988.110336 m² | 258.998811 ha | 640 ac |
| Square meters | 1 m² | 0.0001 ha | 0.000247 ac |
| Square feet | 0.092903 m² | 0.000009 ha | 0.000023 ac |
The acre is 43,560 square feet on the international foot (0.3048 m), which is 4,046.8564224 m²; NIST retired the older U.S. survey foot after 31 December 2022. The hectare is exactly 10,000 m².
When should I not trust a measured area?
If two edges cross, as in a bow-tie, the polygon has no single inside, and the number would not be what the drawing suggests. The tool warns you when that happens; reorder or remove the corners until the outline no longer crosses itself.
The area has no holes: one outline only. To measure a shape with a hole, such as a lake inside a park, load it in the GeoJSON viewer, which subtracts the holes. For a legal boundary, a land sale, a building permit or a crop-subsidy claim, a click on a map is a good estimate and not a survey: use the official record or a licensed surveyor.
Questions about measuring area
How do I find the area of an irregular shape?
Click its corners all around the outline. The polygon closes by itself and the area appears from the third click. Add corners along curved edges to follow them closely.
Is the area on the ground or on a flat map?
Neither exactly: it is the area on the WGS 84 ellipsoid, the smooth model of the Earth, with geodesic edges. It is not distorted like the area measured on a web map, whose scale grows toward the poles.
Does hilly terrain change the result?
Yes, in reality. The tool gives the area projected onto the ellipsoid, as maps and land records do. The true surface of a steep slope is larger than that.
How many acres are in a hectare?
One hectare is 10,000 m², and one acre is 4,046.8564224 m², so a hectare is about 2.4711 acres. The comparison table lists every unit.
Why does the tool warn that the edges cross?
Because the outline touches itself, like a figure eight. The area of such a shape is not what you meant. Change the order of the corners so the outline goes around once.
Can I load the corners of a shape from a list?
Yes. Drop a CSV file of coordinates in the panel, or paste the rows: one corner per row, in the order around the shape, in decimal degrees or degrees-minutes-seconds. Up to 500 corners are read. A row that cannot be read is listed by its line number, and the other corners still draw the shape.
Is the result good enough for a property boundary?
Use it for estimates. Property lines are defined by deeds and surveys, and the tool measures what you click, with the precision of your clicks. Ask a licensed surveyor or the land registry for legal figures.
Sources and limits
- C. F. F. Karney, “Algorithms for geodesics”, J. Geodesy 87 (2013) 43–55
The direct and inverse geodesic algorithms used for distance, bearing, midpoint, circle and polygon area.
Opened and read on .
- World Geodetic System (WGS 84)
Semi-major axis 6 378 137 m, flattening 1/298.257223563, semi-minor axis 6 356 752.314245 m.
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- NIST Guide to the SI, Appendix B.8: conversion factors
Exact factors: mile 1 609.344 m, nautical mile 1 852 m, foot 0.3048 m, yard 0.9144 m, hectare 10 000 m².
Opened and read on .
- NIST, U.S. survey foot: revised unit conversion factors
Acre = 43 560 ft² = 4 046.856 422 4 m² and square mile = 640 acres = 2 589 988.110 336 m² on the international foot, which replaced the survey foot after 31 December 2022.
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- OpenFreeMap
No registration, no API keys, no cookies; commercial use allowed; no limits on map views or requests; attribution required.
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- OpenFreeMap terms of service (updated 9 September 2026)
A free service provided as is, with no warranties; automated collection of data without permission is not allowed.
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- OpenStreetMap copyright and license
Map data is under the Open Database License; credit to OpenStreetMap is required.
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These are calculation aids, not survey instruments. They measure on a mathematical model of the Earth (WGS 84); for a legal boundary, engineering or navigation, use a licensed surveyor or the official chart. Nothing you type or load leaves your browser.
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