The units on a Bihar record
A khatiyan or jamabandi in Bihar writes the area (rakba) of a plot in acre and decimal — the survey units — and people speak of it in bigha, katha and dhur. A sale deed may carry both, and a surveyor's field book is in lattha (laggi) or in feet. Naapi shows all of them at once; this page says what each is and how they relate.
Decimal, acre, hectare — the fixed units
These are the same everywhere in India.
| Unit | Equals |
|---|---|
| 1 acre | 100 decimal = 4,840 square gaj (yards) = 43,560 square feet = 4,046.86 m² |
| 1 decimal (dismil) | 1/100 acre = 435.6 square feet = 48.4 square gaj = 40.4686 m² |
| 1 hectare | 2.4711 acre = 247.11 decimal = 10,000 m² |
| 1 square gaj (yard) | 9 square feet = 0.8361 m² |
The cadastral survey measured every plot with a 66-foot chain (zarib, जरीब) of 100 links (kadi, कड़ी, 7.92 inches each), and 10 square chains make an acre — which is why the record is in acre and decimal.
Bigha, katha, dhur — the local units
Throughout Bihar the counting is fixed:
- 1 bigha = 20 katha
- 1 katha = 20 dhur
- 1 dhur = 20 dhurki
What changes from place to place is the size of the katha, because it is built on the local measuring pole, the lattha or laggi: a katha is 45 square lattha and a dhur is 2¼ square lattha, and the lattha is 5½ feet in one district and 6 or 6½ in another. So the same "one katha" is a different piece of ground in Patna, in Vaishali and in Champaran.
| Where it is used | Lattha | 1 katha | 1 katha in decimal | 1 decimal in dhur | 1 bigha |
|---|---|---|---|---|---|
| Vaishali and neighbouring districts (Naapi's default) | 6½ ft | 1,902.18 sq ft | 4.367 decimal | 4.58 dhur | 87.34 decimal |
| Patna and much of central Bihar | 5½ ft | 1,361.25 sq ft | 3.125 decimal | 6.4 dhur | 62.5 decimal |
| Some districts; Jharkhand, West Bengal | — | 720 sq ft | 1.653 decimal | 12.1 dhur | 33.06 decimal |
The first row is the value Naapi ships with, because 4.58 dhur to the decimal is the working rule of the amins the app was built with. Confirm the value used in your own mauza — ask the local amin, or divide a plot's recorded rakba by its bigha-katha-dhur figure in the same record — and set it in the app's Units fold or in the converter below. Decimal, acre and hectare are unaffected by this choice; only bigha, katha and dhur move.
Converter
Type a value in any unit; the others follow. The three local numbers can be edited, or a preset chosen.
| decimal | 4.37 |
|---|---|
| katha | 1 |
| dhur | 20 |
| bigha | 0.05 |
| acre | 0.0437 |
| hectare | 0.0177 |
| sq ft | 1,902 |
| sq m | 176.7 |
| sq gaj | 211.4 |
| bigha · katha · dhur | 0 · 1 · 0 |
Katha, dhur and bigha follow the local values above; decimal, acre and hectare are the same everywhere.
The formulas an amin uses
- Rectangle: length × breadth.
- Four sides (the amin's average): (north + south) ÷ 2 × (east + west) ÷ 2. Quick, and exact only when the plot is a rectangle; for a skewed plot it overstates the area. Naapi's calculator offers it, and beside it the exact figure from four sides and a diagonal.
- Four sides and one diagonal (exact): the diagonal splits the plot into two triangles; each triangle's area comes from Heron's formula, area = √(s(s−a)(s−b)(s−c)) with s the half-perimeter, and the two are added. Measuring the diagonal from the north-west to the south-east corner is what makes the figure exact.
- Any polygon from the map: the shoelace formula on the corner coordinates — what Naapi uses — checked by triangles and by the kanghi (comb) method of parallel ordinates.
- From square feet to katha: divide by the local square feet per katha; the remainder × 20 ÷ (square feet per katha) is the dhur. From decimal to dhur: multiply by the local dhur per decimal.
Reading a measured area against the record
Because the survey's chain and the local lattha are different rulers, a plot of 1 bigha 4 katha in Vaishali is 104.8 decimal, and the same words in Patna are 75 decimal. When a measured figure and a recorded one disagree, check first which katha the record meant, then the map's scale, and only then the boundary. How to read a mauza naksha goes through the other reasons a measurement differs from the rakba.