Acreage Calculator

What one acre covers

An acre measures area, not shape. It equals 43,560 square feet, the number worth memorizing. Picture a square with the same area and each side runs 208.71 feet, about two-thirds the length of a football field.

The square is where the mental picture breaks down. Two parcels hold the same acreage if their flat area matches, even when one is long and narrow. A lot wrapped around a pond and an L-shaped corner share nothing but the number.

The unit traces to farmland surveying: one furlong by one chain, 660 feet by 66 feet. NIST keeps the acre in its table of conversion factors at 4,046.873 square meters for the survey acre, within a hair of the international 4,046.856.

For scale, an NFL field is 360 feet long with the end zones and 160 feet wide. That is 57,600 square feet, or 1.32 acres. A 0.2 acre suburban lot is 8,712 square feet, less than a sixth of the field.

Listings rarely use square feet. They say 0.46 acre, 2.3 acres, 40 acres, and the calculator turns whatever you have into that language.

Acreage from length and width

For a rectangular parcel, acreage is length times width divided by 43,560. Measure both sides in the same unit, multiply, then divide once at the end. Doing the division last keeps rounding out of the middle of the work.

Most mistakes come from mixed units. A plat map may list feet, a surveyor's note may use chains, and a county GIS page may show meters. Convert everything to feet first, then multiply.

Yards trip people up: a square yard is nine square feet, not three. Fifty by sixty yards is 3,000 square yards, or 27,000 square feet, which is 0.6198 acres.

A 100 foot square is 10,000 square feet, or 0.2296 acres. Double each side and the area quadruples to 40,000 square feet, or 0.9183 acres. Area scales with the square of the length, which is why a lot that looks twice as wide is four times as big.

Worked example: a corner lot and a backyard

Take a corner lot 150 feet along the street and 220 feet deep. Multiply and you get 33,000 square feet. Divide by 43,560 and the lot measures 0.7576 acres, just over three quarters of an acre.

The same area in metric takes one more step. One square foot is 0.09290304 square meters, so 33,000 x 0.09290304 = 3,065.8 square meters. Divide by 10,000 and that is 0.3066 hectares.

Fencing is a separate sum. The distance around the lot is 740 feet, and at $28 per linear foot for a six foot cedar fence that comes to 740 x 28 = $20,720. Acreage says nothing about that number, which is why the calculator prints the perimeter too.

A smaller case: a backyard 80 feet by 120 feet is 9,600 square feet, or 0.2204 acres. A quarter acre is 10,890 square feet, a square 104.36 feet on a side.

Run it backward when a listing gives acreage and you want dimensions. Five acres is 217,800 square feet, a square 466.69 feet on each side with 1,866.76 feet around it. Forty acres is a square 1,320 feet on a side.

Triangles, circles and leftover shapes

Plenty of parcels are not rectangles. A corner cut by a diagonal road is a triangle, and a farm field often steps around a creek. Break the shape into pieces you can name, work each piece, then add them up.

The triangle rule needs a height measured at a right angle to the base. A slanted side is not a height, and using it inflates the answer. In a triangle with sides of 240, 180 and 300 feet, the right angle sits between the two shorter sides, so either can be the base.

A 40 foot radius circle covers 5,026.55 square feet, or 0.1154 acres, with 251.33 feet of edge. The formula fits a full circle, not a lot with a rounded front and straight sides. Sketch that kind of parcel on graph paper and count the squares.

For a shape with no name, draw a line that turns the parcel into two rectangles or a rectangle and a triangle, measure each piece, and add them.

Acres to feet, hectares and square miles

The arithmetic here comes down to a handful of factors. One acre is 43,560 square feet, 4,840 square yards, 4,046.86 square meters, 0.4047 hectares and 0.0015625 square miles. A square mile holds 640 acres.

A hectare is 10,000 square meters, which is 107,639 square feet, or 2.4711 acres, about a square 100 meters on a side. Listings outside the United States use it more than acres.

Small parcels are usually quoted in fractions. A quarter acre is 10,890 square feet, and an eighth is 5,445, roughly a 74 foot square.

Large tracts get quoted in sections and square miles. A square mile is 640 acres, or 27,878,400 square feet. Ten acres is 435,600 square feet, and 100 acres is 4,356,000, or 0.15625 square miles.

Reading a legal description

Rural deeds in the public land states use the Public Land Survey System. The Bureau of Land Management's specifications for land descriptions lay out the grid: a township is a six mile square holding 36 sections, and a section is a one mile square of 640 acres.

Each section splits into halves, quarters and quarters of quarters. The 40 acre quarter-quarter is the unit the BLM treats as standard for management, and it shows up in most oil leases and farm sales.

The northwest quarter of section 14 is 160 acres. The southeast quarter of that northwest quarter is 40 acres, a square 1,320 feet on a side. Add the township and range and a title company can follow it.

One catch: not every section holds exactly 640 acres. Sections along the north and west edges of a township absorb the survey corrections, so they often run short or long and carry lot numbers instead of clean fractions, as the BLM study guide on the survey system explains.

Measuring a parcel yourself

For a house lot, a tape and a helper handle the job. Measure the front and back widths separately, then the two depths, since lots in older subdivisions are rarely perfect rectangles. Average each pair, then multiply.

Small errors in the field turn into bigger errors in the answer. A lot of 200 by 200 feet is 40,000 square feet, or 0.9183 acres. Measure 5 feet long on every side and it becomes 205 by 205, which is 42,025 square feet, or 0.9648 acres. That is a 5.1% jump from a tape that slipped.

Phone apps that walk the boundary with GPS are quick on large tracts and shaky on small ones. A few feet of drift matters little across 40 acres and a lot across a quarter acre. Walk the line twice and compare the readings.

Pay for a survey before you buy, build on or divide a parcel. This calculator is for budgeting and comparing listings, not for recording a deed.

What acreage leaves out

A number in acres describes flat area and stops there. It says nothing about slope, drainage, trees, easements, setbacks or what the zoning code allows. Two lots of 0.76 acres can support wildly different houses.

Setbacks eat the usable space fast. On a 150 by 220 foot lot with a 25 foot front setback, 30 feet in back and 10 feet on each side, the building envelope is 130 by 165 feet, or 21,450 square feet. That is 65% of the lot, before a driveway or a septic field takes its share.

Price per acre is the other number buyers want. At $12,000 an acre, a 0.7576 acre lot costs about $9,091. A $250,000 asking price on 2.3 acres works out to $108,696 an acre, which tells you whether the land or the house carries the value.

Slope is invisible in the acreage figure. Land on a 10% grade rises 10 feet for every 100 feet you walk, so the ground holds more surface than the map shows, and less of it in a shape you can build on.

Lastly, acreage says nothing about access. A 40 acre tract with no road frontage and no recorded easement is hard to use and hard to sell.