How this calculation works
Choose the shape supported by your horizontal measurements. Rectangle mode assumes right angles. A triangle needs three valid sides. A simple quadrilateral needs four boundary sides in order and a measured internal AC diagonal, which splits it into two triangles.
Rectangle: L × W; triangle: Heron’s formula; quadrilateral: area(ABC) + area(ACD)A worked example
A rectangular 30 ft by 40 ft site has 1,200 sq ft, 111.483648 m² and approximately 2.754821 cents. A 30–40–50 ft triangle instead has 600 sq ft. Four different sides alone cannot establish a general plot area.
Good to know
Horizontal plan geometry only, not a certified survey or sloping surface area. Four sides do not uniquely determine a quadrilateral; the measured diagonal must be internal. Feet:inches is a component notation, not a decimal. No inference about location, boundaries, setbacks or buildability.
Reference: NIST: exact international-foot and acre factors (opens in a new tab) ↗
Check the land-unit definitions and sources
The standard factors use the international foot and an acre of 43,560 sq ft. Cent means 1/100 acre; gunta means 1/40 acre; the selected Chennai ground means 2,400 sq ft.
The Assam report defines bigha as 14,400 sq ft, katha as 2,880 sq ft and lecha as 144 sq ft. The cited West Bengal court order mentions a 720-sq-ft katha convention. These are explicit presets, not an automatic definition for every record or every place using the same name. Match your record to the stated convention, or use its verified custom factor.
- NIST: exact international-foot and acre factors (opens in a new tab) ↗
- API Setu MDDS: acre/cent and acre/gunta relationships (opens in a new tab) ↗
- Greater Chennai Corporation: one ground is 2,400 sq ft (opens in a new tab) ↗
- Government of Assam AIRBMP framework: section 7.2, page 28 (bigha, katha and lecha) (opens in a new tab) ↗
- Supreme Court order, 7 May 2025: paragraph 2, page 2 (West Bengal katha) (opens in a new tab) ↗
The acre relationships are converted using exact base factors. Rounded or unrelated regional values in a reference table are not substituted for these definitions.
Four sides leave a quadrilateral free to change shape
Four sides of equal length can form a square or a tilted rhombus. The boundary lengths stay the same while the enclosed area changes. That is why a general four-side plot calculator cannot determine an exact area from those four numbers alone.
This page asks for a measured internal AC diagonal as well as AB, BC, CD and DA. The diagonal forms triangle ABC and triangle ACD. Their three-side areas can be calculated independently and added when the triangles represent opposite sides of that internal diagonal.
A 30 by 40 ft rectangle has a 50 ft diagonal. Each 30–40–50 triangle has area 600 sq ft, so the two give 1,200 sq ft. This is a useful check because the rectangle formula obtains the same result without using a diagonal.
Read feet and inches as components
In feet mode, 30:6 means 30 feet 6 inches, which is 30.5 decimal feet. The value 30.6 instead means 30 feet plus six tenths of a foot, or 30 feet 7.2 inches. Those lengths are different even though their written forms look similar.
For a 30 ft 6 in by 40 ft 3 in rectangle, the product is 30.5 × 40.25 = 1,227.625 sq ft. Inches must remain below twelve in component notation; write 31:0 rather than 30:12. Metres mode accepts ordinary decimal metre lengths.
The simple-polygon area calculator is the more appropriate route when you already have ordered Cartesian survey points. Do not place latitude and longitude degrees into a flat side-length formula. Horizontal plan measurements also differ from distances measured along a slope.
A few questions, answered
Can this work from four sides and no diagonal?
Only if you independently know a restrictive shape such as a rectangle. For a general quadrilateral, supply the measured internal diagonal; no average-opposite-sides approximation is substituted.
What if three supplied sides do not meet?
The tool rejects a triangle when the sum of its two shorter sides is not greater than the longest. Collinear zero-area triangles are rejected too.
Does the area certify the boundary?
No. Arithmetic does not establish the record, measured boundary, accuracy or legal extent. Those require the relevant survey and record checks.