Plot Area Calculator
Measure your plot’s sides, add one diagonal if it has four unequal sides, and the plot area calculator gives the area in sq ft, m², square yards (gaj), acres, hectares and regional land units. If you measured a corner angle instead of a diagonal, enter the four sides and that angle. Odd shapes can be entered as triangles, and every step of the sum is shown.
Plot area calculator
Planning aid: the area on your title deed or survey is the one that counts. Sloping land: enter horizontal distances.
Bare numbers are meters; 66 ft works too.
- Plot area
- 450 m²
- Perimeter (boundary sides)
- 90.00 m (295′ 3″)
The plot measures 450 m², exactly.
Other units
- ≈ 4,843.76 sq ft
- ≈ 538.20 sq yd
- ≈ 0.1112 acres
- 0.045 ha (exact)
How this was calculated
- Rectangle: area = width × depth
- Triangle (Heron): s = (a + b + c) ÷ 2; area = √(s(s − a)(s − b)(s − c))
- Four sides + diagonal AC: area = triangle ABC + triangle CDA (a convex plot)
- Four sides + angle A: BD = √(AB² + DA² − 2·AB·DA·cos A); area = ½·AB·DA·sin A + Heron(BC, CD, BD) (a convex plot)
- Triangles: area = sum of the triangles
- Area = 15 m × 30 m = 450 m² (exact)
How the calculator works it out
Rectangles
Front width × depth. With exact factors, a 30 × 40 ft plot is 1,200 sq ft = 111.483648 m² with no rounding.
Triangles
Heron’s formula gives a triangle’s area from its three sides: s = (a + b + c) ÷ 2, area = √(s(s − a)(s − b)(s − c)). The square root is rounded, so these results carry ≈.
Four-sided plots
The diagonal AC splits the plot into triangles ABC and CDA. Their areas add up to the plot’s.
Four sides and one angle
With the angle at corner A, the law of cosines gives the diagonal BD = √(AB² + DA² − 2·AB·DA·cos A). Triangle ABD is ½·AB·DA·sin A, triangle BCD comes from Heron’s formula, and the two add up.
Any unit
The area is converted to sq ft, m², square yards (gaj), acres and hectares, or to a regional unit for the region you pick.
Rectangular plots
Measure the front (the side on the road) and the depth. Multiply them: a 30 × 40 ft plot is 1,200 sq ft, 133⅓ sq yd (gaj) and 111.483648 m². In meters, a 15 × 30 m plot is 450 m².
Check that the plot is a rectangle: when both pairs of opposite sides are equal and the two diagonals are equal, the corners are square. If not, enter the plot as four sides and one diagonal.
Irregular plots: why you need a diagonal
Four sides alone don’t fix a plot’s shape. Push two opposite corners together and the sides keep their lengths while the area shrinks. A diagonal locks the shape: with AC measured, triangles ABC and CDA each have three known sides, and each has one area. One measured corner angle does the same job: choose “Four sides + one corner angle” and enter the inside angle at A, between sides DA and AB. If sides BC and CD are too short to reach across the diagonal that angle gives, the calculator says so instead of giving an area.
The calculator assumes a convex plot, one with no corner pointing inwards. If a corner points inwards, enter the plot as triangles instead.
Splitting a plot into triangles
Pick a corner
Stand at one corner and measure to every corner you can see across the plot. Each pair of neighbouring lines and the boundary between them forms a triangle.
Write down three sides each
For every triangle note its three sides. Shared lines appear in two triangles; use the same figure both times.
Enter one row per triangle
Choose “Split into triangles” and add a row for each. The calculator adds their areas and reports any three sides that can’t form a triangle.
Worked examples
A four-sided plot with AB 20 m, BC 30 m, CD 25 m, DA 28 m and diagonal AC 36 m: triangle ABC ≈ 300.00 m², triangle CDA ≈ 348.86 m², so the plot is ≈ 648.86 m², ≈ 6,984.23 sq ft, ≈ 776.03 sq yd and ≈ 0.1603 acre.
With a corner angle instead: AB 30 m, BC 25 m, CD 28 m, DA 20 m and 85° at A. The diagonal BD = √(30² + 20² − 2 × 30 × 20 × cos 85°) ≈ 34.575 m. Triangle ABD = ½ × 30 × 20 × sin 85° ≈ 298.86 m², triangle BCD ≈ 345.90 m², so the plot is ≈ 644.76 m². In feet, AB 60, BC 50, CD 55 and DA 40 ft with 95° at A is ≈ 2,570.24 sq ft, about 0.0590 acre.
A rectangle 30 × 40 ft is 1,200 sq ft = 133⅓ sq yd = 111.483648 m². A right-angled triangle with sides 60, 80 and 100 ft is 2,400 sq ft = 222.967296 m².
Measuring on site vs reading a layout plan
On site, measure horizontal distances along the boundary: on a slope, hold the tape level or the sides come out too long. Measure each side twice and use the average.
On a layout plan, use the written dimensions where there are any. If you have to scale a length off the drawing, the floor plan scale calculator turns a measured paper length into a real one.
Plot area in gaj, acres and hectares
The area shows in square feet or square meters by default; pick square yards (gaj), acres, hectares or a regional unit under “Show the area in”. Sizes of regional units differ by state and district and have changed over time; your land record is the authority.
Frequently asked questions
How do I calculate the area of an irregular plot?
Split it into triangles and add their areas. For a four-sided plot, measure the four sides and one diagonal; for more sides, measure from one corner to the others. Heron’s formula gives each triangle’s area from its three sides.
Why is a diagonal needed for a four-sided plot?
Four sides can make many shapes with different areas, like a hinged frame. The diagonal fixes the shape, splitting it into two triangles whose areas are fixed by their sides. One corner angle fixes it too, so you can enter the four sides and the angle at one corner instead.
How do I calculate plot area in square feet?
For a rectangle, multiply the front by the depth in feet: 30 × 40 ft is 1,200 sq ft. For other shapes, enter the sides here and read the square feet figure.
How do I convert plot area to gaj or acres?
Divide square feet by 9 for gaj (square yards) and by 43,560 for acres. The calculator shows all of them, plus hectares and regional units.
Which measurement counts if mine differs from the deed?
The figure on your title deed or official survey is the one that counts. A difference can come from slope, measuring to a different line, or an error on either side; a licensed surveyor can settle it.
Ready to plan your space?
It is free, runs in your browser and needs no account. Projects are saved privately on this device.