Article — Acreage Calculator
The acreage calculator, plain and exact
An acreage calculator converts plot dimensions to land area in acres. The base formula is simple: area in square feet divided by 43,560 equals acres. A rectangular lot 300 ft by 200 ft contains 60,000 sqft, which works out to 1.377 acres. The calculator above runs that math for rectangles, circles, and triangles, and presents the result in acres, square feet, hectares, square meters, and square miles at once.
The number 43,560 is a defined constant, fixed by NIST Handbook 44 and recognized in every US property deed. Once you know the formula, the math is arithmetic. The harder part is measuring the dimensions accurately, which is why most real-world acreage values come from surveyors, not tape measures.
How acreage is measured
Land area is the horizontal projection of the plot, not the surface area along the terrain. A steep mountainside reads smaller on the deed than it does underfoot, because the deed measures the parcel as if it were laid flat. Government surveys use this convention so that adjoining parcels add up exactly to the township or section total.
Dimensions can come from any of three sources: a hand-paced measurement (rough, ±5%), a tape or laser measure (good for small lots, ±1%), or a professional survey using GPS or total stations (±0.5 ft). Real estate transactions need the third source; the first two are fine for planning a garden or estimating a fence run.
The Britannica entry on the acre notes that the medieval English acre was originally defined as the area one yoke of oxen could plow in a single day. The shape was always a long, narrow strip — 40 rods by 4 rods (660 ft by 66 ft) — because turning a plow team at the end of a row was the slowest part of the work, so plowmen preferred long runs.
Calculating acreage from a rectangle
Most surveyed lots are rectangles. Multiply length by width in feet, divide by 43,560, and you have the acreage. A few examples worth keeping in mind:
- 100 × 100 ft = 10,000 sqft = 0.2296 acres (suburban quarter-acre)
- 150 × 100 ft = 15,000 sqft = 0.3444 acres (larger suburban)
- 200 × 200 ft = 40,000 sqft = 0.9183 acres (just under one acre)
- 208.71 × 208.71 ft = 43,560 sqft = exactly 1.000 acre (square acre)
- 300 × 200 ft = 60,000 sqft = 1.377 acres (small rural homesite)
- 500 × 500 ft = 250,000 sqft = 5.739 acres (hobby farm)
- 1,000 × 1,000 ft = 1,000,000 sqft = 22.96 acres (small commercial farm)
- 5,280 × 5,280 ft = 27,878,400 sqft = 640 acres (exactly 1 square mile)
Calculating acreage for a round parcel
Circular plots are common in the US Midwest, where center-pivot irrigation systems water round fields. The formula uses π times the radius squared, then divides by 43,560.
A circle with a 117.75-ft radius is exactly 1 acre. A quarter-section center-pivot system has a radius of about 1,320 ft and covers roughly 125.7 acres — a few acres less than the 160-acre quarter-section it sits in, because the circle leaves four small corners untouched. Some farms install corner-watering attachments to recover those acres.
r = 117.75 ft ⇒ 1.00 acre r = 166.51 ft ⇒ 2.00 acresr = 263.27 ft ⇒ 5.00 acres r = 1,320 ft ⇒ 125.7 acresTriangle and irregular acreage
For a triangular lot, multiply the base by the perpendicular height, divide by 2, then divide by 43,560. A wedge-shaped corner lot with a 200-ft base and a 150-ft height is 200 × 150 / 2 = 15,000 sqft, or 0.344 acres.
Irregular plots are handled by decomposition. Sketch the boundary, divide it into rectangles and right triangles, calculate each piece, and add the acreages. For lots with curved boundaries (along a river, road curve, or shoreline), GIS software computes the exact area from a digital boundary file. The USGS National Map Viewer offers free measurement tools that work this way for any US property visible on aerial imagery.
When a plot's boundaries are described in "metes and bounds" (the old English-style deed format with compass bearings and chain lengths), the surveyor's report should already give the acreage. If you only have the bearings, use the surveyor's coordinate method: convert each segment to (dx, dy), then apply the shoelace formula. The math is in any introductory surveying textbook.
Acreage in acres, hectares, and square meters
The calculator presents acreage in four units simultaneously. Outside the US, UK, Canada, India, and a handful of other countries, hectares are the standard agricultural unit. 1 hectare equals 10,000 square meters or 2.471 acres. The US average farm size in the 2022 USDA Census of Agriculture is 463 acres, which converts to 187 hectares — large by European standards, where Eurostat reports the median farm size at just 17.4 hectares.
Typical acreage values worth memorizing
Memorize three numbers and you can sanity-check any acreage figure you encounter.
- 10,000 sqft ≈ 0.23 acres. A suburban lot. Common across most US metros.
- 43,560 sqft = 1 acre exactly. The reference point. About 209 ft square.
- 640 acres = 1 sq mile exactly. The PLSS section unit. Townships are 36 sections, 23,040 acres.
The Bureau of Land Management still administers federal lands using the PLSS framework, so any rural deed west of the Appalachians describes its location in terms of township, range, and section.
Mistakes when computing acreage
The classic mistake is mixing units. A deed that gives one side in feet and the other in meters cannot be multiplied directly. Convert everything to feet first (1 m = 3.2808 ft), then apply the area formula.
The second mistake is using the slant distance along sloping ground instead of the horizontal distance. A 200-ft tape pulled across a 20 percent slope reads 200 ft, but the horizontal projection is closer to 196 ft. Surveyors correct for this. Tape-and-pace measurements should be corrected on steep ground, or treated as approximate.
A house listed as "3,200 sqft" refers to heated floor area, not the lot. The lot acreage is a separate field on the deed. Confusing the two has caused more than one buyer to pay residential prices for what they thought was a much larger parcel. Always read the deed, not just the listing.
Acreage precision and survey accuracy
Professional land surveyors are expected to produce acreage figures accurate to 0.01 acre or better for residential parcels. A typical residential survey costs $300 to $1,000 in the US; larger or more complex boundaries push the price into the thousands. The accuracy comes from differential GPS (cm-level) and total stations (mm-level over short distances), neither of which is available to most homeowners.
For unofficial work, the USGS National Map provides aerial-imagery measurement tools accurate to about ±3 ft per side, which translates to 1 to 2 percent error on a residential lot. That is more than enough to confirm whether a quoted acreage figure is plausible. For anything that affects a real estate transaction, however, a current professional survey is the only acceptable source.