EstimatorKitFree acre calculator
Acres from a lot line, and back to feet
An acre is 43,560 square feet exactly, and it has no shape of its own: squared off it is 208.71 ft a side, while the original acre was a strip 66 ft wide and 660 ft long. This free calculator works in three directions — lot dimensions into acres, any figure converted between acres, square feet, square yards, square meters, hectares and square miles, and an irregular parcel taken from the four boundary lengths a deed lists. No signup, nothing uploaded, and when four side lengths genuinely cannot fix an area it says so instead of quietly choosing one.
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- 43,560 sq ft to the acre
- 6 area units
- Deed parcels bounded
A rectangular lot you have paced, taped or read off a plat. Frontage runs along the road; depth runs back from it.
Distances default to feet and take a unit when you write one: 208.71, 264 ft, 70 yd or 63.6 m straight off a metric plan. A plat given in chains needs converting first — one chain is 66 ft.
That parcel is
0.4591 acres
- Square feet
- 20,000
- Square yards
- 2,222
- Square meters
- 1,858
- Hectares
- 0.1858
- Square miles
- 0.000717
Shapes that hold this much
Squared off it is 141.42 ft a side, or 141' 5" on a tape. An acre on its own squares up at 208.71 ft — 208' 8 1/2" — but the original acre was a strip 66 ft wide and 660 ft long, and land arrives in whatever shape the boundaries left it.
The boundary itself runs 600 ft, which is the figure a fence or a survey crew is priced on rather than the acreage.
The units land is written in
Every one of these still turns up on a deed, a plat or a listing, and each was a round number to whoever coined it. Reading them in square feet is what makes them look random.
| Unit | Square feet | Where the number comes from |
|---|---|---|
| Acre | 43,560 | One chain by one furlong — 66 ft × 660 ft, the strip a team of oxen was reckoned to plow in a day. |
| Square chain | 4,356 | Gunter's surveying chain of 66 ft, squared. Ten of them make an acre, which is why the acre is a round number in chains and an ugly one in feet. |
| Square rod | 272.25 | A rod is 16.5 ft, a quarter of a chain. There are 160 square rods to the acre, and old deeds still quote them. |
| Hectare | 107,639.1 | 10,000 square meters, so 2.4710538 acres. The unit every metric land registry uses. |
| Section (square mile) | 27,878,400 | 640 acres. The base tile of the Public Land Survey grid that most of the US west of Ohio is cut into. |
| Quarter section | 6,969,600 | 160 acres — the claim size the Homestead Act of 1862 handed out, and still the shape of a lot of section-line farmland. |
| Quarter-quarter section | 1,742,400 | 40 acres, the smallest unit the original survey subdivided to. This is the back forty of the expression. |
How to work out acreage
Three starting points, because land arrives described three different ways.
Say which of the three you are starting from
Two dimensions if you have taped or paced a rectangular lot; a figure to convert if a listing gave you hectares and the county wants acres; four deed boundaries if all you have is the length of each side of an irregular parcel. They ask for different things because they are different problems, and the third one has an answer the other two do not need.
Enter the boundary the way it was written down
Distances default to feet and accept a written unit, so 208.71, 264 ft, 70 yd and 63.6 m all land correctly, and a plat drawn in chains converts at 66 ft each. In convert mode the figure takes thousands separators and fractions, so 43,560 square feet and 2 1/2 acres both go in as typed.
Read the acreage, then check it against a shape you can walk
The result comes back in acres with square feet, square yards, square meters, hectares and square miles under it, plus the side length that parcel would have if it were squared off and the distance round the boundary — which is the figure a fence or a survey crew prices, not the acreage. Turn on the setback panel and it also shows what is left inside the front, rear and side lines to build on.
Technical specifications
| Acre in square feet | 43,560 exactly — ten square chains, fixed by definition rather than measured |
|---|---|
| An acre squared off | 208.71 ft a side, or 208' 8 1/2" on a tape |
| The acre's original shape | 1 chain × 1 furlong, which is 66 ft × 660 ft |
| Metric | 1 acre = 0.404686 ha = 4,046.8564224 m²; 1 hectare = 2.4710538 acres |
| Section | 640 acres to the square mile, or 27,878,400 sq ft |
| Irregular parcels | Ceiling from the four boundary lengths, printed beside the average-of-sides rule and the gap between them |
| Input modes | Three: two dimensions, a figure in any of six units, or four deed boundaries |
| Sent anywhere | No — lot dimensions and boundary lengths never leave this browser |
Frequently asked questions
Why is an acre 43,560 square feet rather than a round number?
Because it was defined as a shape, not an area: one chain by one furlong, which is 66 ft by 660 ft. The furlong was a furrow-long, the distance a team of oxen could pull a plow before needing a rest, and the chain was the width of plowed ground that went with it. In the units of the people who set it the acre is perfectly round — ten square chains, or 160 square rods. It only looks arbitrary once it is written in feet.
What are the dimensions of an acre?
An acre has no dimensions, only an area. Poured into a square it is 208.71 ft a side, which is 208 ft 8 1/2 in on a tape; laid out in its historical proportions it is 66 by 660 ft; as a strip along a road with 100 ft of frontage it runs 435.6 ft back. All four describe the same acre, which is why any picture of one is a picture of a choice somebody made.
How many acres is a 100 by 200 foot lot?
0.4591 acres — 20,000 square feet divided by 43,560. That is the most common suburban lot in the country and it is worth remembering as slightly under half an acre, because it makes the rest of the scale easy: a quarter-acre lot is about 10,890 square feet, and a lot advertised as half an acre should measure about 21,780.
Can I get the acreage of an irregular parcel from the four side lengths alone?
No, and any tool that gives you a single number for it is guessing. Four fixed lengths still hinge like a jointed frame: push one corner in and the area falls while every boundary stays exactly the length the deed says. What can be calculated is the ceiling — the largest area those four sides can enclose, which happens when all four corners fall on one circle — and the deed mode shows that alongside the old average-of-opposite-sides rule, which can never read low and matches the truth only on a rectangle. One diagonal off a plat closes the gap for good.
How many acres are in a hectare?
2.4710538, and in the other direction an acre is 0.404686 hectares. Both are exact rather than rounded conversions, because the international foot has been defined as precisely 0.3048 m since 1959, which fixes the acre at 4,046.8564224 square meters. A hectare is simply a square 100 m on a side, so unlike the acre it does have a natural shape.
Is a US survey acre different from an international acre?
Yes, by four parts in a million, and it stopped mattering on 31 December 2022 when NIST and the National Geodetic Survey retired the US survey foot. That foot was two parts per million longer, which made a survey acre 4,046.8726 square meters against the international 4,046.8564 — about 10 square meters across a full 640-acre section, and nothing at all across a house lot. Deeds written from older state plane coordinates can still carry it.
How much of an acre can actually be built on?
Whatever is left after the setbacks, and it is usually far less than people expect. A 100 by 200 ft lot with a 25 ft front setback, a 25 ft rear and 10 ft each side leaves an envelope of 80 by 150 ft — 12,000 of the 20,000 square feet, or 60 percent — and that is the outer limit before any lot-coverage cap, easement, septic field or drainage rule takes its share. The setback panel in the tool does this arithmetic with your own ordinance's numbers, since ours would be wrong in every jurisdiction but one.
About the acre and how land is described
The acre survives because it was never really a number — it was a day of work. A furlong is a furrow long, the run a plow team could manage before resting, and a chain was the matching width of ground. Multiply the two and you get 43,560 square feet, which looks like a random figure only because it is being expressed in a unit nobody involved was using. In chains it is ten; in rods it is 160. That history is still in the ground: the Public Land Survey cut most of the country into square-mile sections of 640 acres, split them into quarters of 160 and quarter-quarters of 40, which is why so much rural land comes in those exact sizes and why a road grid a mile apart is the normal spacing across the Midwest.
The question hiding inside almost every search for this is a shape question, not an area one. People want to know how far an acre goes along a road, or whether a lot they are standing on is the half-acre it was sold as, and an area alone cannot answer either. Give this page a frontage and it returns the depth; give it two dimensions and it returns the distance round the boundary, which is what a fence contractor and a survey crew both price from — an acre with 100 ft of frontage carries 1,071 ft of fence line, while the same acre laid square carries 835. Long thin parcels cost more to enclose and to serve with a drive, and the acreage on the listing says nothing about which one you are buying.
The hardest case is an old deed with four boundary lengths and no diagonal, and the honest response is a bound rather than an answer: four fixed sides still flex, so the tool reports the largest area they could enclose and the older average-of-opposite-sides rule beside it, with the gap between them shown as the least the rule is wrong by. Once an acreage is settled, the work moves off this page: fence line, driveway edging and boundary run are lengths and belong on the linear feet calculator, anything spread across the ground needs a depth before it becomes a delivery, which is square feet to cubic yards, and a bank of ground that has to be held back is the retaining wall calculator. For the house that goes on the lot rather than the lot itself, the square footage calculator measures inside the walls and follows an entirely different rulebook.
Where your lot dimensions stay
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
Boundary lengths off a deed identify a specific piece of ground, which is reason enough for them not to be collected. There is no account here to attach them to and no request leaves the page while you type.