Before you pay for land, it helps to know whether the plot on the ground matches the plot on paper. A professional survey is the final word, but you can get a good first check yourself with a measuring tape, a few pegs and a little arithmetic. This guide shows how to measure and calculate the area of regular and irregular plots.
What you need
- A long measuring tape, 30 metres or 100 feet, or a laser distance meter.
- Four or more pegs or stones to mark corners.
- A helper to hold the other end of the tape.
- A notebook and a phone for photographs.
- The documents: sale deed, survey sketch and revenue record.
Step 1: Mark the corners
Walk the boundary with the owner and the neighbours and agree where each corner is. Place a peg at each corner, and take a photograph of each peg with something nearby for reference. If neighbours disagree about a corner, stop and settle it first: nothing you calculate will help if the boundary itself is disputed.
Step 2: Measure each side
Keep the tape straight, taut and level. If the ground slopes, measure the horizontal distance, not the distance along the slope. Measure every side twice and record the average. Use the same unit throughout: feet or metres, not a mix.
Step 3: Check that corners are square
For a rectangular plot, measure both diagonals. If the plot is a true rectangle, the two diagonals are equal. To set out a right angle from a corner, use the 3-4-5 method: measure 3 units along one side, 4 units along the other, and adjust until the distance between those two points is 5 units. Multiples work too, such as 6-8-10 or 30-40-50 feet.
Rectangle or square
Area = length × breadth. A plot of 40 ft by 30 ft has an area of 1,200 sq ft. That is 133.3 sq yd, since 1,200 ÷ 9 = 133.3, and about 111.5 sq m.
Triangle
If you know the base and the height measured at right angles to it: area = ½ × base × height. A triangle with a base of 30 ft and a height of 20 ft has an area of 300 sq ft.
If you only know the three sides, use Heron’s formula. Let the sides be a, b and c, and let s be half the total of the three. Then area = √(s × (s − a) × (s − b) × (s − c)). For sides of 30, 40 and 50 ft, s = 60, so the area = √(60 × 30 × 20 × 10) = √360,000 = 600 sq ft.
Trapezium
When two sides are parallel, which is common for plots along a straight road, area = ½ × (sum of the parallel sides) × the distance between them. If the parallel sides are 50 ft and 30 ft and they are 40 ft apart, the area is ½ × 80 × 40 = 1,600 sq ft.
Irregular plots: divide and add
Most real plots are not perfect shapes. The method is to split the plot into rectangles and triangles, measure each one, and add the areas.
- Sketch the plot and draw lines from corner to corner, dividing it into simple shapes.
- Measure the base and height of each piece, and for triangles also record all three sides if you want to double check with Heron’s formula.
- Calculate each area, then add them.
Example: an L-shaped plot is split into a 40 ft × 30 ft rectangle (1,200 sq ft) and a right triangle with a base of 30 ft and a height of 20 ft (300 sq ft). The total is 1,500 sq ft, which is about 166.7 sq yd or 139.4 sq m.
Step 4: Convert to the unit in the documents
Your answer will probably be in square feet or square metres, while the sale deed may say cents, guntha, or bigha. Convert using the factors in our guide on converting acres to square feet. For regional units such as bigha and katha, read why they differ first.
Step 5: Compare with the paper
A small difference of a percent or two can come from tape error and boundary wear. A larger gap means something is wrong: a part of the plot may belong to a road or a neighbour, the document may be wrong, or your measurements may have an error. Repeat the measurements. If the difference persists, ask a licensed surveyor to measure the plot and sign a report, and do not close the deal until the area is settled in writing.
Limits of a DIY measurement
- Tape measurements are less accurate on rough ground and long distances.
- Phone map apps are fine for a rough idea, but they are not accurate enough for a purchase.
- Only a government or licensed survey will be accepted in disputes.
Once you have your area, the Plotwise converter can show it in every common unit, and the price calculator can turn it into a cost. Use it as a planning tool and rely on official records for any legal decision.