Land Plot Area Calculator
Area of a four-sided plot with unequal sides, in bigha, katha, guntha, acre or hectare.
This tool runs entirely in your browser. Your data is never uploaded, never stored, and never leaves your device.
Works out the area of a four-sided plot whose sides are all different lengths, and — unlike most tools that do this — says plainly when four sides alone are not enough to give an answer.
How to use it
- 1Number the sides in order as you walk the boundary and enter all four.
- 2Measure one diagonal, corner to opposite corner, and enter it: this is what makes an exact answer possible.
- 3Read the area in acres, hectares, bigha, katha, guntha or any other listed unit.
- 4If you have no diagonal, the other tab gives the largest area those sides could enclose, labelled as a bound rather than an answer.
Example
- Input
- Sides of 100, 80, 110 and 75 feet with a 110 ft diagonal (the built-in defaults)
- Output
- 7,731 sq ft — 0.177 acre, or 0.284 bigha pucca
The same four sides with no diagonal give an upper bound of 8,118 sq ft. The real plot is 4.8% smaller. Change the diagonal to 165 ft and it drops to 6,318 — 22% below the bound — with the sides untouched.
What happens to your data
The diagonal splits the plot into two triangles and each is measured with Heron's formula, so a result with a diagonal is exact rather than an estimate. Impossible measurements are rejected rather than silently returning a number. Everything is computed in the page and nothing you type is sent anywhere.
Last updated September 2026
Four side lengths do not tell you the area of a plot. That is not a technicality — it is the entire problem, and most calculators that do this quietly pretend otherwise.
Pin four sticks together at the corners and the frame still flexes. The sides never change; the area does. Sides of 100, 80, 110 and 75 feet can enclose 8,118 square feet or 6,318 depending only on how bent the plot is, a difference of 22%, and nothing about the four numbers tells you which.
So this asks for one more measurement: a diagonal, corner to opposite corner. That pins the shape down. The diagonal splits the plot into two triangles, each triangle is measured exactly, and the answer is the real area rather than an estimate — 7,731 square feet for those sides with a 110 foot diagonal, which is 0.177 acre or 0.284 pucca bigha.
If you genuinely have only the four sides, the other tab still gives you a number, but labelled honestly: the largest area those sides could possibly enclose. Most tools give you that figure and call it the answer.
How it works
With a diagonal, Toolvore splits the plot into two triangles — sides 1 and 2 with the diagonal, then sides 3 and 4 with the same diagonal — and applies Heron’s formula to each. Heron gives the exact area of a triangle from its three sides alone, because unlike a quadrilateral a triangle IS fixed by its sides: there is nothing left to flex. Add the two and you have the plot.
Measurements that cannot describe a real plot are rejected rather than quietly returning something. If the diagonal is longer than the two sides beside it put together, or shorter than the difference between them, no triangle closes, and the page says so and suggests where to re-check. That is usually a mistyped digit or a paced distance, and being told beats being given a plausible wrong number.
Without a diagonal the page uses Brahmagupta’s formula, the square root of (s−a)(s−b)(s−c)(s−d). That is exact only for a cyclic quadrilateral — one whose four corners happen to sit on a circle — and for every other shape with those sides it returns more than the truth. What it actually computes is the maximum: the cyclic arrangement is the one that encloses the most area, which is why the result is shown as “at most” and explained rather than presented as the area.
Lengths are accepted in feet, metres, gaj or surveyor’s links, and the result can be read in any of the land units — acre, hectare, bigha in its several sizes, katha, biswa, guntha, cent, dismil, marla, kanal, ground or square feet — all derived from their own definitions rather than copied, so a dismil and a cent read the same because they are the same.
Two real limits worth knowing. The arithmetic assumes flat ground: a plot on a slope encloses less level land than its sides suggest, because the sides are measured along the slope and the area is not. And it assumes straight boundaries, so a curved edge has to be broken into shorter straight runs and added up. All of it is computed in the page; nothing is uploaded and nothing you type is stored.
Common use cases
- Working out the area of a farm plot whose four sides are all different lengths
- Checking a figure quoted by a seller or a neighbour against your own measurements
- Converting a measured plot straight into bigha, katha or guntha for a land record
- Finding out that four sides alone were never going to give an answer, before relying on one
- Spotting a mistyped measurement, because impossible shapes are rejected rather than averaged over
Frequently asked questions
Why do you need the diagonal? Other calculators do not ask for it.＋
Because without it there is no answer to give. Four sides do not determine a quadrilateral — the shape can flex while the sides stay the same, and the area changes as it does. With these defaults, a 110 foot diagonal gives 7,731 square feet and a 165 foot diagonal gives 6,318, on identical sides. A calculator that asks only for four sides is either returning the maximum possible area or an average of something, and is not telling you which.
What does the number in the four-sides tab actually mean?＋
It is the largest area those four sides could enclose, which happens when the four corners lie on a circle. Any other arrangement of the same sides encloses less. So read it as a ceiling: your plot is that size or smaller, usually smaller. For the built-in example the ceiling is 8,118 square feet and the real plot with a 110 foot diagonal is 7,731 — 4.8% under. On a more bent plot the gap reaches 22%.
Which diagonal should I measure?＋
Either one, as long as you know which sides it separates. Number the sides in order as you walk the boundary, then measure from the corner between sides 2 and 3 across to the corner between sides 4 and 1 — that diagonal separates sides 1 and 2 from sides 3 and 4, which is how the tool splits the triangles. Measuring the other diagonal and entering it here gives a wrong answer, because it would be splitting the plot a different way.
It says my measurements cannot form a plot.＋
Then one of them is wrong, and that is worth knowing. For a triangle to close, any two sides must together be longer than the third. If the diagonal is longer than sides 1 and 2 put together, or shorter than the difference between them, no such shape exists. In practice this is a mistyped digit or a paced distance that drifted — re-measure the diagonal and the two sides on either side of it.
Does it work for a plot with more than four sides?＋
Not directly. Split the plot into triangles or four-sided pieces yourself, measure each, and add the results. That is what a surveyor does with an irregular boundary, and it is more reliable than trying to average a complicated shape into four numbers.
Can I use this figure for a sale or a land record?＋
Treat it as arithmetic rather than authority. The calculation is exact for the measurements you give it, but the measurements themselves are the weak link — sloping ground, a curved boundary, or a tape that was not pulled straight all change the answer more than the formula does. For anything that has to be right in law, the land record and a licensed surveyor are the authority.
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