Land measurement guide
How to calculate acreage
Calculating acreage comes down to one step everyone forgets and one constant nobody has to memorize twice: find the area in square feet, then divide by 43,560. This guide walks the math for a plain rectangle, for the irregular shapes real parcels actually take, and for measuring a boundary in the field, then shows the shortcut that skips the arithmetic entirely.
The one formula: square feet to acres
There are exactly 43,560 square feet in an acre, and that never changes. So every acreage calculation ends the same way:
acres = total square feet ÷ 43,560
Everything else is just finding the total square feet. Going the other direction, square feet equals acres times 43,560. Work in feet throughout and the units take care of themselves.
Rectangles and squares
For a rectangular parcel, area is length times width in feet, then divide by 43,560. Say a field is 330 feet by 660 feet:
- 330 ft × 660 ft = 217,800 square feet
- 217,800 ÷ 43,560 = 5.0 acres
Irregular shapes
Real parcels are rarely tidy rectangles. The reliable method is to break the shape into pieces you can measure, usually rectangles and right triangles, find each area, and add them up before the final divide.
- Rectangle: length × width.
- Right triangle: one-half × base × height. A triangle is half of the rectangle that would enclose it.
- Trapezoid: average the two parallel sides, then multiply by the distance between them.
For the field on the right above, suppose the rectangle part is 180 ft by 100 ft (18,000 sq ft) and the triangle on top has a 180 ft base and a 30 ft height (one-half × 180 × 30 = 2,700 sq ft). Total is 20,700 square feet, and 20,700 ÷ 43,560 is about 0.48 acres. When a boundary is given as corner coordinates rather than side lengths, the surveyor's method, also called the shoelace formula, computes the polygon area directly, which is what mapping software does under the hood.
Square feet to acres, at a glance
A quick reference for common sizes. Every row is just the row's square footage divided by 43,560, so you can interpolate between them.
| Square feet | Acres | Common example |
|---|---|---|
| 10,890 | 0.25 | Quarter acre, a common suburban lot |
| 21,780 | 0.50 | Half acre |
| 43,560 | 1.00 | One acre |
| 87,120 | 2.00 | Two acres |
| 217,800 | 5.00 | Five acres, a small homesite |
| 435,600 | 10.0 | Ten acres |
Measuring a boundary in the field with GPS
If you do not have the dimensions, you can gather them by walking the boundary. A mapping or land-measurement app records a point at each corner as you go, closes the polygon, and reports the enclosed area. A few honest cautions:
- Treat it as an estimate. Consumer phone GPS is typically accurate to within a few meters, and on a small lot that error can shift the acreage by a real fraction.
- Corners matter more than the walk. A clean reading at each true corner beats a wandering track along the edge.
- It is not a survey. For a fence, a sale, or a dispute, the legal answer comes from a licensed survey, not a phone.
The shortcut: draw it and let the map do the math
The fastest accurate method skips hand arithmetic altogether: outline the parcel on a map and let software compute the area from the polygon. It handles any shape, avoids reading and multiplication errors, and gives the same answer the shoelace formula would. AgriTerra works exactly this way. You draw or tap the boundary, and it returns the computed acreage alongside the parcel's soil, water, flood, and revenue data, so the acreage arrives with the rest of the picture rather than on its own.
For the ideas behind the numbers, see how big an acre is, how sections and quarter-sections are sized, what a plat map records, and how much an acre of land costs.
Calculating acreage: frequently asked questions
- How do you calculate acreage?
- Find the area in square feet, then divide by 43,560, because there are 43,560 square feet in an acre. For a rectangle, area is length times width. For an odd shape, split it into rectangles and triangles, add their areas, then divide by 43,560.
- How many square feet are in an acre?
- Exactly 43,560 square feet. So acres equals square feet divided by 43,560, and square feet equals acres times 43,560. For example, 20,000 square feet is 20,000 divided by 43,560, which is about 0.46 acres.
- How do I calculate the acreage of an irregular lot?
- Break the lot into simple shapes whose area you can find, usually rectangles and right triangles, using the boundary dimensions. Add the pieces to get total square feet, then divide by 43,560. If you have corner coordinates instead of side lengths, mapping software can compute the area directly from the polygon.
- Can I measure acreage with my phone GPS?
- Roughly, yes. A mapping app can record corner points as you walk a boundary and compute the enclosed area. Treat the result as an estimate: consumer GPS is usually accurate to within a handful of meters, which can move a boundary calculation by a noticeable amount on a small lot. For anything legal, use a licensed survey.
- What is the fastest way to get an accurate acreage?
- Outline the parcel on a map and let software compute the area from the polygon. That avoids hand arithmetic and reading errors, and it works on any shape. AgriTerra computes acreage this way from the boundary you draw, alongside the parcel's soil and other data.
Skip the arithmetic. Draw the parcel.
Outline any parcel and AgriTerra computes its acreage from the boundary, alongside soil, water, flood, and revenue options, from federal data, free.