Plot Size Calculator
Measure the four sides of the plot and one diagonal between opposite corners. The calculator splits the plot into two triangles, finds each area and adds them up.
- Any four-sided shape
- Uses Heron's formula
- m², ft², acres, hectares
Label the corners in order going round the plot. The diagonal runs from the corner between sides a and d to the corner between sides b and c.
Four sides are not enough to know the area. A plot with sides of 30, 40, 30 and 40 metres could be a 1,200 m² rectangle or a squashed shape of half that. The diagonal fixes the shape. With it, the plot splits into two triangles whose areas can be found exactly.
Common plot sizes
Typical residential plots. Search for a size.
| Plot | Dimensions | m² | sq ft | Acres |
|---|---|---|---|---|
| Small UK plot | 10 × 25 m | 250 | 2691 | 0.06 |
| 5 marla | 25 × 45 ft | 105 | 1125 | 0.03 |
| 10 marla | 35 × 65 ft | 211 | 2275 | 0.05 |
| 1 kanal | 50 × 90 ft | 418 | 4500 | 0.1 |
| US city lot | 50 × 100 ft | 465 | 5000 | 0.11 |
| US suburban lot | 80 × 135 ft | 1003 | 10800 | 0.25 |
| Quarter acre | 1,012 m² | 1012 | 10890 | 0.25 |
| Half acre | 2,023 m² | 2023 | 21780 | 0.5 |
| One acre | 4,047 m² | 4047 | 43560 | 1 |
Plot sizes vary widely by country. In South Asia plots are often sold in marla and kanal; one marla is about 25.3 m² and one kanal is 20 marla.
Same sides, different areas
A plot with sides 30, 40, 30 and 40 m. Slide the diagonal.
This is why surveyors measure diagonals or angles. A deed that lists only four side lengths does not tell you the true area.
How to measure a plot
Five measurements and two triangles. Step through it.
Mark the corners
Label them A, B, C and D going round.
Use a long tape or a laser measure, and keep it level. On sloping ground the horizontal distance is what counts for area.
Tape, GPS or survey
Three ways to find a plot's size. Compare the methods.
Sides and a diagonal measured by hand. Cheap and accurate on small, flat plots.
Walk the boundary or trace it on a map. Quick but can be several metres out.
Professional instruments tied to official boundary records.
For buying, selling or building, rely on a licensed survey. A tape measure is fine for planning a garden or estimating materials.
Before buying a plot
Size is one of several checks. Tick each item.
Tick each item as you go.
Building rules usually limit how much of a plot you can cover, often 50% to 70%, and set gaps to the boundary. The usable area can be much less than the total.
What you get
The area in every common unit. Each tile explains one result.
In the unit you measured in.
Metric area.
For US and UK listings.
For larger land.
The parts that make up the total.
The triangle areas let you check the result by hand, and show how the plot splits along the diagonal.
Frequently Asked Questions
No question matches that search.
How do I calculate the area of an irregular plot?
Measure the four sides and one diagonal, split it into two triangles and add their areas using Heron's formula.
Why do I need the diagonal?
Because four side lengths can form many shapes with different areas. The diagonal fixes the shape.
How many square feet are in an acre?
43,560 square feet, or about 4,047 m².
How big is a marla?
Usually 272.25 sq ft (25.3 m²), though some areas use 225 or 250 sq ft.
How do I measure a plot with five or more sides?
Split it into triangles from one corner, measure the diagonals, and add up each triangle's area.
Does slope affect plot area?
Legal plot area is the flat horizontal area. Measure horizontally, not along the slope.
Can I work out area from a rectangle's sides?
Yes, multiply length by width. For a true rectangle the diagonal will be √(length² + width²).
Know the true size of your land
Measure four sides and one diagonal, and the calculator gives the exact area of any four-sided plot. Use it to check a listing, plan a build or estimate materials, and get a professional survey before any legal step.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.