The Irregular Land Area Calculator calculates the acreage of a lot, field or parcel that is not a neat rectangle.
Enter the boundary corners as coordinates (shoelace formula), or enter four sides plus one diagonal (the lot is split into two triangles and each is solved with Heron’s formula). Results are shown in acres, hectares, square feet and square meters, along with the boundary length for fencing. A quick-estimate mode averages opposite sides when you only have four side lengths.
Irregular Land Area Calculator (Acreage)
Acreage of an irregular lot or field from boundary coordinates or from four sides and a diagonal — in acres, hectares, ft² and m².
Sides a and b meet the diagonal at one end, sides c and d at the other.
The averaging method is only a rough estimate and overstates the area when corners are far from square. Add a diagonal for an accurate figure.
Formula
Boundary coordinates
A = ½ |Σ (xᵢyᵢ₊₁ − xᵢ₊₁yᵢ)|
Four sides and a diagonal
A = T₁ + T₂, where each triangle T = √(p(p − x)(p − y)(p − z)) and p is half its perimeter
Quick estimate
A ≈ ((front + back) ÷ 2) × ((left + right) ÷ 2)
Acres = square feet ÷ 43,560; hectares = square meters ÷ 10,000.
How the Calculation Works
Step 1: Get the boundary from a survey plat, deed, or your own measurements.
Step 2: Enter it as corner coordinates, or as four sides plus the diagonal between the a/b corner and the c/d corner.
Step 3: The calculator finds the area in square feet or meters and converts it to acres and hectares.
Variables Explained
| Input | Meaning | Unit |
|---|---|---|
| x, y | Corner positions along two perpendicular directions | ft, m, yd |
| a, b, c, d | Boundary sides in order | ft, m |
| Diagonal | Line joining two opposite corners | ft, m |
| Area | Land area | acres, ha, ft², m² |
Example Calculation
From coordinates
Given: corners (0, 0), (420, 0), (460, 310), (60, 350) in feet
Area: 136,300 ft² ÷ 43,560
Result: ≈ 3.129 acres; boundary ≈ 1,489.67 ft
From four sides and a diagonal
Given: sides 420, 312.6, 402 and 355.1 ft; diagonal 502.1 ft
Result: ≈ 136,305 ft² ≈ 3.129 acres (matching the coordinate result)
Quick estimate
Averaging the same four sides gives ≈ 3.150 acres — slightly high, because the corners are not square.
Land Area Conversion Table
| Unit | Equivalent |
|---|---|
| 1 acre | 43,560 ft² = 4,046.86 m² |
| 1 hectare | 10,000 m² ≈ 2.471 acres |
| 1 square mile | 640 acres |
| 1 km² | 100 ha ≈ 247.1 acres |
Shape Properties
Why the diagonal matters
Four side lengths do not define a four-sided lot — the corners can lean and change the area. One diagonal fixes the shape exactly. Averaging sides ignores the angles and generally overstates the area, which is why that mode is labeled an estimate.
Lots with more corners
For five or more corners, use the coordinates mode and list every corner in order.
Dimensions Explained
Turning a plat into coordinates
Pick one corner as (0, 0). Measure how far each other corner is east (x) and north (y) of it. If your plat gives bearings and distances, each leg’s east and north components can be added up to get the coordinates.
Results are for planning and estimating. Legal boundaries and official acreage come from a licensed surveyor.
Frequently Asked Questions
How do you calculate the acreage of an irregular lot?
Find the area in square feet (coordinates, or triangles from sides and diagonals) and divide by 43,560.
How many square feet are in an acre?
43,560 ft².
Can I find the area of land with just four sides?
Only approximately. For an exact answer, add one diagonal or use corner coordinates.
How do I find the area of a triangular lot?
Use Heron’s formula with the three side lengths, or enter the three corners as coordinates.
How much fencing do I need for my lot?
Use the perimeter from the coordinates mode, then subtract gates or sides you won’t fence.
