Plot Area Calculator (West Bengal units)

Quick answer: For a plot with four unequal sides, measure the four sides and one diagonal, split it into two triangles, and add their areas (Heron's formula). Then divide sq ft by 720 for katha or by 435.6 for decimal.

How to measure your plot

1. Name the corners. Walk round the plot and call the corners A, B, C and D in order.
2. Measure every side. Pull the tape tight and straight along the boundary, from corner to corner.
3. Measure one diagonal. For a four-sided plot, measure from corner A to corner C, across the inside of the plot. This one length fixes the shape. Without it, the area of a four-sided plot cannot be worked out.
4. Use one unit. Take every length in the same unit (all in feet, or all in metres). Convert inches to a decimal of a foot: 6 inches is 0.5 ft.
5. Measure each side twice. If the two readings differ, measure a third time and use the figure that repeats.

How the area is calculated

Every length is first turned into feet. Then:

• Rectangle: area = length × width.
• Triangle (Heron's formula): s = (a + b + c) ÷ 2, and area = √(s × (s − a) × (s − b) × (s − c)). If the longest side is equal to or longer than the other two added together, the sides cannot make a triangle, and the calculator says so.
• Four sides and a diagonal: the diagonal AC cuts the plot into triangle ABC and triangle ACD. Each is solved with Heron's formula, and the two areas are added.
• Trapezium: area = (parallel side 1 + parallel side 2) ÷ 2 × height, where the height is the straight-across gap between the two parallel sides.

The area in square feet is then converted with the West Bengal units: 1 chatak = 45 sq ft, 1 katha = 16 chatak = 720 sq ft, 1 bigha = 20 katha = 14,400 sq ft, 1 decimal (satak) = 435.6 sq ft and 1 acre = 100 decimal = 43,560 sq ft.

Why not average the sides? Four sides alone do not fix a plot's shape: push one corner and the same four sides enclose less land. The "average length × average width" shortcut assumes square corners. On a slanted plot it always gives too much area. Only use it as a rough check on a plot that is almost a rectangle.

Worked example

A plot has sides AB = 60 ft, BC = 40 ft, CD = 62 ft and DA = 38 ft, and the diagonal AC = 72 ft.

• Triangle ABC (60, 40, 72): s = 86. Area = √(86 × 26 × 46 × 14) = √14,39,984 ≈ 1,199.99 sq ft.
• Triangle ACD (62, 38, 72): s = 86. Area = √(86 × 24 × 48 × 14) = √13,87,008 ≈ 1,177.71 sq ft.
• Total ≈ 2,377.71 sq ft = 3 katha 4.84 chatak ≈ 5.46 decimal.

Open this example in the calculator.

Sources and conventions

• West Bengal land units as used across this site (1 bigha = 20 katha = 14,400 sq ft; 1 katha = 720 sq ft; 1 decimal = 435.6 sq ft). See West Bengal Land Measurement Units Explained and the land measurement converter.
• Gunter's chain = 66 ft = 100 links, so 1 link = 0.66 ft: NIST Handbook 44, Appendix C (General Tables of Units of Measurement).
• 1 metre = 3.2808 ft (1 ft = 0.3048 m exactly). 1 yard = 3 ft.
• Conventions last checked on 15 October 2026. The local haat (cubit) is not offered because we found no official West Bengal length for it.

This is an estimate from your own measurements. The legal area of a plot is the one in its khatian (record of rights) and deed. For a sale, a dispute or boundary fixing, have the plot measured by a licensed surveyor (amin), for example through your BL&LRO (Block Land and Land Reforms Office). Plot records are on banglarbhumi.gov.in.

Rates and conventions last checked: 15 October 2026.