What the Acreage Calculator does
This acreage calculator measures a plot of land in acres, hectares, square feet and square metres - plus guntha, cents, kanal, marla and bigha - from its length and width, from four unequal sides, or from a list of corner coordinates taken with a phone or GPS. Next to every answer it names the method used and says whether the figure is exact for your measurements or only an estimate.
Most real plots are not rectangles, and that is where land area goes wrong: four side lengths alone do not fix the area of a four-sided plot. Adding one diagonal, or two corner angles, makes the answer exact; with sides only, the calculator gives the largest area those sides could enclose and says so. Everything runs in your browser - corner coordinates are not sent anywhere and no map is loaded.
How to use it
- Choose how you measured the plot: length and width, four sides, or corner coordinates.
- For four sides, walk round the boundary and enter the sides in order, then say what else you measured: the diagonal from corner A to corner C gives an exact area, as do the angles at those two corners. If you only have the sides, choose "Nothing else" for an upper estimate.
- For coordinates, paste one corner per line in order round the plot - latitude and longitude in decimal degrees from a phone map, or x and y from a survey plan.
- Pick the length unit, and the bigha used in your area if you need bigha.
- Read the area in acres at the top and every other unit in the table. The perimeter is shown for fencing.
Reading the results
"Exact" here means exact for the numbers you entered. A 1% error in each side becomes about a 2% error in the area, so careful measurement matters more than decimal places.
"Up to" in front of the answer means you gave four sides and nothing else. The real plot can be noticeably smaller if its corners are far from square; measure one diagonal to remove the doubt.
Units such as guntha, cents, kanal and marla are fixed fractions of an acre and are the same everywhere they are used. The bigha is not: its size differs from state to state and sometimes district to district, so the calculator always shows how many square feet of bigha it used.
Worked example: a four-sided field with one diagonal measured
A field has sides of 420, 310, 395 and 290 feet in order, and the diagonal from corner A to corner C is 530 feet. The diagonal splits it into a triangle with sides 420, 310 and 530 and another with sides 395, 290 and 530.
For the first, half the perimeter is s = (420 + 310 + 530) / 2 = 630 and Heron's formula gives √(630 x 210 x 320 x 100) = 65,066 sq ft. For the second, s = 607.5 and the area is √(607.5 x 212.5 x 317.5 x 77.5) = 56,361 sq ft. Together, 121,427 sq ft.
Dividing by 43,560 sq ft per acre gives 2.79 acres, which is 1.13 hectares, about 111.5 guntha, or 8.43 West Bengal bigha of 14,400 sq ft. With the four sides alone the calculator would say "up to 2.80 acres" - close here because this field's corners are nearly square.
Formulas and scoring rules
- Rectangle
A = length x width- Four sides and a diagonal
A = Heron(a, b, p) + Heron(c, d, p), where Heron(x, y, z) = √(s(s - x)(s - y)(s - z)) and s = (x + y + z) / 2- Four sides and two opposite angles (Bretschneider)
A = √((s - a)(s - b)(s - c)(s - d) - a b c d cos²((A + C) / 2)), s = (a + b + c + d) / 2- Four sides only (Brahmagupta, maximum)
A_max = √((s - a)(s - b)(s - c)(s - d))Equal to the true area only when opposite corners add up to 180 degrees. The average-of-opposite-sides rule, (a + c) / 2 x (b + d) / 2, is shown beside it and is never smaller.- Corner coordinates (shoelace)
A = ½ |Σ (x_i y_(i+1) - x_(i+1) y_i)|GPS corners are first projected to metres: x = N cos φ0 Δλ, y = M Δφ, with M and N the WGS84 radii of curvature at the plot's centre latitude φ0.- Units
1 acre = 43,560 sq ft = 4,046.8564224 m²; 1 ha = 10,000 m²; guntha = 1/40 acre = 1,089 sq ft; cent = 1/100 acre = 435.6 sq ft; kanal = 1/8 acre = 5,445 sq ft; marla = 1/160 acre = 272.25 sq ft
Bigha, guntha, cent and kanal - regional land units
In India, Pakistan, Bangladesh and Nepal land is often recorded in local units. The guntha (used in Maharashtra, Karnataka, Telangana and Gujarat) is 1/40 of an acre; the cent (Kerala and Tamil Nadu) is 1/100 of an acre; the kanal and marla (Punjab, Haryana, Himachal Pradesh, Jammu and Kashmir) are 1/8 and 1/160 of an acre.
The bigha has no single size. In West Bengal and Assam it is commonly 14,400 sq ft (20 katha of 720 sq ft); the Rajasthan pucca bigha is 27,225 sq ft (165 ft square); other states use other values, and some districts differ again. The two presets name their value, and "Custom" accepts the figure from your own land records.
Measuring corners with a phone
Stand on each corner in turn, drop a pin in your map app, and copy its latitude and longitude. Phone GPS is typically good to a few metres in open sky, so on a small plot the corner positions, not the arithmetic, limit the accuracy: a 3 m error on each corner of a one-acre square can move the area by several percent. For anything legal, use the surveyed boundary.
Limitations: what the result does not prove
- It measures flat (horizontal) area. On sloping ground the surface is larger than the area shown, and land records also use horizontal area.
- Four sides without a diagonal or angles give only the maximum possible area. Do not use that figure for a sale or a boundary dispute.
- Bigha and other local units vary by region and over time; check the value used in your land records before relying on a bigha figure.
- The coordinate method uses a flat local projection that is accurate for plots up to a few kilometres across. It is not a cadastral survey, and phone GPS error dominates on small plots.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- NIST SP 811 - Guide for the Use of the International System of Units - checked 19 Sep 2026
- NIST - US survey foot and international foot (acre definitions)
- NGA - World Geodetic System 1984 (WGS 84) parameters
- Wolfram MathWorld - Bretschneider's formula
- Wolfram MathWorld - Brahmagupta's formula
Frequently asked questions
How do I calculate acres from feet?
Multiply the length by the width in feet to get square feet, then divide by 43,560. A plot 330 ft by 132 ft is 43,560 sq ft, which is exactly 1 acre. For an irregular plot, enter its four sides and a diagonal instead.
How do I find the area of a plot with four unequal sides?
Measure the four sides and one diagonal. The diagonal splits the plot into two triangles whose areas Heron's formula gives exactly; the calculator adds them. With the sides alone the area is not fixed, so you only get an upper limit.
Can I calculate land area from GPS coordinates?
Yes. Paste each corner's latitude and longitude in order round the plot, one per line. The calculator projects them onto a flat plane using the WGS84 ellipsoid and applies the shoelace formula, all in your browser.
How many square feet are in a bigha?
It depends on the state. A West Bengal or Assam bigha is commonly 14,400 sq ft and a Rajasthan pucca bigha 27,225 sq ft, while other regions use different values. Choose a preset or enter your local value under Custom.
How many guntha make one acre?
Forty. A guntha is 1/40 of an acre, which is 1,089 sq ft or about 101.17 square metres, so 1 acre = 40 guntha and 1 hectare is about 98.8 guntha.
Is the average of opposite sides method accurate for land?
Only for plots that are close to rectangles. Multiplying the average of each pair of opposite sides never gives less than the true area and overstates it when corners are far from square. A diagonal measurement gives the exact figure.
What is the difference between an acre and a hectare?
A hectare is 10,000 square metres; an acre is 4,046.86 square metres. One hectare is about 2.471 acres, and one acre is about 0.405 hectares.
Last reviewed by the A2Z.Tools team against the sources listed above.
