Field Area (Irregular Plot) Calculator

Work out field area (irregular plot) instantly with clear inputs, formula shown and shareable results.

About Field Area (Irregular Plot) Calculator

For a four-sided field measured only along its boundary, the cyclic-quadrilateral (Bretschneider/Brahmagupta) form gives the largest area those four sides can enclose: sqrt((sp-a)(sp-b)(sp-c)(sp-d)) where sp is the semi-perimeter. Real plots enclose slightly less, so treat this as an upper bound and split badly skewed fields into triangles.

Formula

Brahmagupta area

sp = (a+b+c+d)/2; Area = sqrt((sp-a)(sp-b)(sp-c)(sp-d))

Worked example

With the default values below, Field Area (Irregular Plot) Calculator returns Field Area of 1,907.30. Change any input above and every figure here is recalculated in your browser.

Inputs used

Side Aminimum 0.1 m: 45 m
Side Bminimum 0.1 m: 38 m
Side Cminimum 0.1 m: 52 m
Side Dminimum 0.1 m: 41 m

Results

Field Area: 1,907.30
Area In Acres: 0.4713
Area In Hectares: 0.1907
Perimeter (fencing length): 176.00

Step by step

1Values used
2Brahmagupta area
3Field Area= 1,907.30
4Area In Acres= 0.4713
5Area In Hectares= 0.1907
6Perimeter (fencing length)= 176.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does my result differ from the survey record?

The formula assumes the quadrilateral is cyclic, which maximises area for the given sides. Any other shape with the same sides encloses less, so a survey using diagonals or GPS will usually read lower.

How do I handle a five-sided or curved field?

Split it into triangles from one corner, measure each triangle's three sides and add the Heron areas, or walk the boundary with a GPS app and use the polygon area it reports.