Area of an irregular plot from its sides, a diagonal or a map
This land area calculator finds the area of a plot or field whose four sides are all different — the usual case for village land, farm fields and many town plots. Enter the four side lengths and one diagonal (or one corner angle) and it splits the plot into two triangles, applies Heron’s formula to each and adds them. For more corners, or with only a map, switch to corner points: paste latitude–longitude pairs, type offsets, or click the corners on the map.
The answer is shown in square feet, square metres, gaj (square yards), acres and hectares, and in the local units of the state you pick — bigha, biswa, katha, guntha, cent, ground, marla, kanal and more. Every local size comes from the same table as the area converter, with its source shown under the selector.
How to use the Land Area Calculator
- Name the corners A, B, C and D in order as you walk around the plot, and measure the four sides AB, BC, CD and DA.
- Measure one diagonal, the straight distance from corner A to corner C across the plot. If that is blocked, measure the angle at corner B instead.
- Type the five measurements and choose the unit — feet, metres, yards, karam or chains.
- Pick your state and the unit you want, then read the area, the working and the table of every unit.
- For a plot with five or more corners, or to measure from a map, choose Corner points / map, then paste coordinates or click the corners in order.
Land Area Calculator features
Two-triangle method
Heron’s formula on triangles ABC and ACD, with every step shown and impossible diagonals caught.
Explains the shortcut error
Shows the largest area your four sides allow and how far the “average of opposite sides” rule overstates your plot.
Map and GPS corners
OpenStreetMap loads only when you open it. Click the corners, or add your phone’s GPS position at each corner where the browser allows location.
Ellipsoid-accurate
Latitude–longitude polygons are measured on the WGS84 ellipsoid, not a flat map.
Local land units
Gaj, guntha, cent, bigha, katha, marla and kanal by state, with cited sources.
Why four sides are not enough
A triangle is rigid: three sides fix its shape and area. A four-sided plot is not. Picture four sticks joined at the corners — you can push the frame from a rectangle into a thin diamond without changing any side, and the area shrinks as you do. So no calculator can give a true area from four sides alone; anything that claims to is assuming a shape.
One extra measurement removes the freedom. The diagonal AC divides the plot into triangles ABC and ACD whose three sides are all known, so each area follows from Heron’s formula: s = (a + b + c) ÷ 2 and area = √(s(s − a)(s − b)(s − c)). The angle at B works too, because it fixes the diagonal through the law of cosines, AC² = AB² + BC² − 2·AB·BC·cos B — this is the same result Bretschneider’s formula gives.
Measure the diagonal that runs inside the plot; if a corner points inwards, use the diagonal from that corner or switch to corner points.
Worked example
A plot has sides AB = 60 ft, BC = 40 ft, CD = 55 ft, DA = 42 ft and diagonal AC = 72 ft. Triangle ABC has s = 86 and area √(86 × 26 × 46 × 14) ≈ 1,200.0 sq ft; triangle ACD has s = 84.5 and area ≈ 1,150.8 sq ft. The plot is about 2,350.8 sq ft, or 261.2 gaj, or 0.054 acre. The popular shortcut ½(60 + 55) × ½(40 + 42) gives 2,357.5 sq ft — close here, but on a skewed plot it can be several per cent too high, because it is exact only for rectangles.
Corner points, maps and GPS
With x, y offsets the calculator uses the shoelace formula. With latitude and longitude it converts each latitude to its authalic (equal-area) latitude on the WGS84 ellipsoid and sums the strips between corners; for plot-sized edges this differs from true geodesic edges by far less than any GPS error. Corners entered out of order make the boundary cross itself, and the tool warns you.
Clicked points are only as good as your zoom and the map, and a phone GPS fix is usually good to a few metres — on a 2,000 sq ft plot that can change the area by more than 10%. Use the map for fields and estimates, and a tape or a licensed surveyor for small plots. The map uses OpenStreetMap tiles (© OpenStreetMap contributors) through the Leaflet 1.9.4 library (BSD-2-Clause), loaded only when you press the button. Nothing you enter is uploaded.
Limits
- This is a calculator, not a survey. The area in your registered sale deed, khatauni, 7/12 or RTC is the legal one.
- Local unit sizes vary by state and sometimes by village; values without a government source are marked “confirm locally”.
- Sides are treated as straight lines. For a curved boundary, add more corner points along the curve.
Land Area Calculator FAQ
How do I calculate land area with 4 different sides?
Measure the four sides and one diagonal, split the plot into two triangles along the diagonal, find each triangle’s area with Heron’s formula and add them. The calculator does this for you and shows the working.
Can I find the area from four sides only?
Not exactly. The same four sides fit many shapes with different areas. The tool shows the largest possible area for your sides, but you need a diagonal or one corner angle for the real figure.
How do I get the plot area in gaj?
Choose “Gaj (square yards)” in the unit list. One gaj is 9 sq ft, so a 2,350.8 sq ft plot is about 261.2 gaj.
Can I measure land area on a map?
Yes. Choose Corner points / map, open the map, zoom in and click each corner in order. You can also paste coordinates copied from any map app, one corner per line.
How accurate is measuring with phone GPS?
Usually within a few metres per point, which is fine for a large field but can be 10% or more off for a small house plot. Stand still on each corner and check the accuracy figure shown.
Which bigha does the calculator use?
The one for the state or district group you select — Rajasthan alone has five — or your own size under Custom.