GIS Acreage Calculator: How to Measure Land Area

A GIS acreage calculator computes the area of a parcel or polygon in acres from its dimensions or coordinates. You enter either the length and width in feet or meters, or a set of GPS coordinates, and the calculator returns the area in acres, along with square feet and square meters for reference. The result is based on standard geometric formulas, so it is exact for rectangles and approximate for irregular shapes.

Formula

The calculator uses the basic rectangle area formula:

Area (acres) = (Length × Width) / 43,560

• Length – the longer side of the parcel, in feet
• Width – the shorter side of the parcel, in feet
• 43,560 – the number of square feet in one acre

If you measure in meters, first convert to feet (1 meter = 3.28084 feet), or use the square-meter output and divide by 4,046.86 (square meters per acre).

Worked Example

Using the default values: Length = 208.71 ft, Width = 208.71 ft.

1. Multiply length by width: 208.71 × 208.71 = 43,560.46 sq ft (rounded).
2. Divide by 43,560: 43,560.46 ÷ 43,560 = 1.00001 acres.
3. The calculator rounds to 4 decimal places, giving 1.0000 acres.

This matches the expected result: a square 208.71 feet on each side is almost exactly one acre.

When to Use a GIS Acreage Calculator

This tool is handy for real estate, farming, land planning, and outdoor projects. You might use it to:

• Check the size of a residential lot before buying or selling
• Estimate the area of a field for seeding or fencing
• Verify a property description from a deed or survey
• Plan a garden, solar array, or driveway footprint

For rectangular parcels, the result is exact. For oddly shaped land, the rectangle method gives a rough estimate; use a GIS software or a polygon-based calculator for better accuracy.

How to Measure Irregular Shapes

Most real parcels are not perfect rectangles. If you have a polygon, you can still get a good acreage estimate using the surveyor’s formula (shoelace formula) if you have coordinates:

1. List the vertices in order (clockwise or counterclockwise).
2. For each vertex (x_i, y_i), compute x_i × y_i+1 – x_i+1 × y_i.
3. Sum all those values, take the absolute value, and divide by 2.
4. The result is in square units; convert to acres by dividing by 43,560 (if using feet) or 4,046.86 (if using meters).

This method works for any straight-sided polygon and is what many GIS tools use internally.

Common Mistakes and Unit Mix-Ups

The most frequent error is mixing feet and meters. Always convert to a single unit before calculating. Other pitfalls include:

• Using the diagonal instead of length and width – the diagonal is longer and gives a wrong area.
• Forgetting that an acre is 43,560 sq ft, not 40,000 or 44,000.
• Rounding too early – keep full precision until the final step.
• Assuming all parcels are rectangles – a 200 ft × 200 ft square is 0.918 acres, not 1 acre.

If you get a result that seems too large or small, double-check your measurements and units.

Limits of the Rectangle Method

This calculator assumes a rectangle. For triangles, trapezoids, or curved boundaries, the rectangle formula overestimates or underestimates. For example, a triangular lot with a 300 ft base and 200 ft height has an area of 0.689 acres, while a rectangle with the same dimensions would give 1.377 acres – double the actual size. For precise legal descriptions, always rely on a licensed surveyor.

Frequently Asked Questions

How many square feet are in an acre?

Exactly 43,560 square feet. This comes from the international acre definition: one acre equals 4,046.8564224 square meters, which converts to 43,560 square feet.

Can I use this calculator for circular land?

No, the rectangle formula does not apply to circles. For a circular parcel, use the formula π × r² (where r is the radius) and then divide by 43,560 to get acres. For example, a circle with a 100 ft radius is 0.721 acres.

What is the difference between GIS acreage and survey acreage?

GIS acreage is calculated from digital maps and coordinates, often using the shoelace formula. Survey acreage is measured on the ground with specialized equipment and accounts for curvature and boundary markers. Survey results are legally binding; GIS values are estimates for planning.

How do I convert acres to hectares?

One acre equals 0.404686 hectares. Multiply the acre value by 0.404686 to get hectares. Conversely, divide hectares by 0.404686 to get acres.

Why does my deed say a different acreage than this calculator?

Deeds often use historical measurements, rounded values, or include easements and rights-of-way. Also, the parcel may not be a perfect rectangle. The calculator gives a mathematical estimate; the deed reflects the legal description.

Does the calculator work for metric measurements?

Yes, if you enter meters, the calculator converts to square meters and then to acres. However, the length and width fields are labeled in feet, so you must convert meters to feet first (multiply by 3.28084) or use the square-meter output and divide by 4,046.86 yourself.

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in length | Length | ft | 208.71 | 0
in width | Width | ft | 208.71 | 0
out acres | Area in acres | acres | (length * width) / 43560 | 4
out sqft | Area in square feet | sq ft | length * width | 2
out sqm | Area in square meters | sq m | (length * width) * 0.092903 | 2