How this instrument works
Katha is not one unit; it is five or more, and none of them agrees with the others closely enough to share a single conversion factor. In West Bengal and Bangladesh, a katha is fixed at 720 square feet. Cross into Bihar and the figure shifts again by district — roughly 1,361 square feet around Patna, and 1,742.24 square feet in Saran district of that same state; Gorakhpur, just across the state line in Uttar Pradesh, happens to share Patna's 1,361-square-foot figure rather than Bihar's own Saran number. Assam fixes its unit at 2,880 square feet, four times the Bengal size, and Nepal's Terai plains use 3,645 square feet — over five times larger than the number quoted two countries away. A calculator that silently applied any one of these to every visitor would return the right area for one region and a wrong one, sometimes by a factor of five, for everybody else. That is why this page makes you pick a region before it will compute anything: there is no honest default to fall back on.
These gaps are not arbitrary; they are leftovers from how British-era revenue survey fixed local land units district by district rather than nationally. Bengal's survey settled its bigha at 14,400 square feet and split it into 20 equal shares of 720 square feet each, and that same ratio carried into what became Bangladesh after partition. Assam's own settlement kept an identical 14,400-square-foot bigha but divided it into only 5 shares rather than 20, so each Assamese share ended up four times the Bengal size from a subdivision choice alone. Bihar's settlement never applied one figure across the state — Patna landed on one scale, Saran on another, and neighboring Gorakhpur in Uttar Pradesh happened to land on Patna's scale despite being a different state altogether — and Nepal's Terai plains, surveyed under a separate bigha-kattha-dhur chain unrelated to British India's settlement, landed on yet another number. Nobody since has unified them, because land records, sale deeds and local custom in each district still run on whatever figure got fixed generations ago.
That legacy still shapes real transactions today. A khatian, parcha or sale deed quoting '5 katha' in a Kolkata suburb, a Patna colony and a Kathmandu tract describes three genuinely different areas, not one plot measured three ways — and a buyer, lender or builder converting that figure to square feet for a mortgage application or a construction quote needs the district's own value, not a textbook number. Many quick online tools quietly hardcode 720 square feet, the West Bengal and Bangladesh figure, because it is the one most often searched, which hands anyone in Bihar, Assam or Nepal a confidently wrong square footage with no hint that anything went astray. Selecting your region here is not an extra step; it is the entire calculation, since the multiplier it sets varies far more than the entered number ever does.
- Enter your plot size into the Katha field — it opens at 5, a common small-plot figure.
- Pick your Region first: West Bengal/Bangladesh, Patna (Bihar)/Gorakhpur (UP), Saran district (Bihar), Assam, or Nepal — each carries its own sq-ft-per-katha figure.
- Read the converted area from Square feet beneath it; it recalculates the instant either the Katha or the Region field changes.
- The page opens already showing 5 katha in West Bengal/Bangladesh at 3600.00 square feet, so you can watch the region's effect before touching a single field.
- Not sure which region applies? Check the district printed on your sale deed or land record rather than guessing — size is a local custom here, not a national standard.
Worked example — 5 katha in West Bengal / Bangladesh
A residential plot in Kolkata, or just across the border in Bangladesh, is advertised as 5 katha. Enter 5 into Katha and leave Region on its default, West Bengal / Bangladesh; Square feet reads 3600.00 — five units at 720 square feet each comes to exactly 3,600 square feet, with nothing left to round since both inputs are whole numbers.
Change only the Region to Patna, Bihar / Gorakhpur, Uttar Pradesh, leaving the entered number at 5, and Square feet jumps to 6805.00 — nearly double the Bengal answer for an identical '5 katha' that might have come off a different sale deed. Switch Region again to Nepal and that same figure of 5 reaches 18225.00 square feet, more than five times the first answer, which is the entire reason this page asks for a region before it computes anything at all.
Questions
Why doesn't katha convert to square feet with one universal factor?
Because it was never standardized nationally — British-era revenue survey fixed a local size district by district, and no government since has unified the results. West Bengal and Bangladesh use 720 square feet, Assam uses 2,880, Nepal uses 3,645, and Bihar alone splits into two different figures depending on district. Applying any single number to every visitor would be correct for one region and wrong, sometimes by a factor of five, for the rest — which is why this page requires picking a region before it computes.
How big is a katha in West Bengal and Bangladesh?
720 square feet, fixed when British-era survey standardized the Bengal bigha at 14,400 square feet and split it into 20 equal shares. That same 20-share bigha and 720-square-foot share carried over into what is now Bangladesh after partition, so both sides of the border still use the identical figure today — one of the few places where the size actually agrees across a modern national boundary.
Why does Bihar have two different sizes for the same unit?
Because British-era settlement was carried out district by district rather than statewide, and Bihar's districts were never later reconciled to a single figure. Around Patna, one share runs about 1,361 square feet — a figure that neighboring Gorakhpur, just across the state line in Uttar Pradesh, happens to share — while Saran district, within Bihar itself, uses 1,742.24 square feet, roughly 28 percent larger for an identically labelled plot. A sale deed or land record from one district cannot be safely read using another district's figure, Bihar or not.
How much bigger is a Nepali katha than a Bengali one?
About five times bigger. Nepal's Terai plains fix it at 3,645 square feet, against 720 square feet in West Bengal and Bangladesh — the widest gap among the regions this page covers. The two share a name and a common South Asian ancestry in pre-metric land survey, but converting a Nepali land listing using the Bengal figure would understate the true area by roughly 80 percent.
Which region should I pick if my document doesn't say?
Check the district named on the sale deed, khatian or parcha itself rather than guessing from the word alone, since the word by itself carries no size information. If the document names a Bihar district, note whether it falls near Patna or in Saran, since those two areas disagree by roughly 28 percent — and if it names Gorakhpur, that district sits just across the state line in Uttar Pradesh but shares Patna's 1,361-square-foot figure. A local land-registry office or the surveyor who prepared the document can confirm which figure was used when the plot was originally measured.
Is Assam's version related to Assam's bigha the way Bengal's is?
Yes, but by a different ratio. Assam's British-era settlement also fixed a 14,400-square-foot bigha, the same size as Bengal's, but divided it into 5 shares rather than 20 — so each Assamese share works out to 2,880 square feet, four times Bengal's, even though the bigha behind both is identical in area. It is a reminder that the bigha, not its subdivision, is often the more stable figure regionally; the split into smaller shares is where the size diverges.
Does this page cover every regional size that exists?
No — it covers five documented, commonly cited figures: West Bengal/Bangladesh, the Patna/Gorakhpur tract spanning Bihar and Uttar Pradesh, Bihar's Saran district, Assam, and Nepal's Terai. Related local units appear under other names and slightly different sizes in additional districts and older records beyond these five, so a plot description from outside these regions is worth confirming against local land-registry practice rather than matched to the nearest option here.
Once I pick the right region, how precise is the square-feet answer?
As precise as the number you entered and the regional factor itself, both of which are customary figures rather than physical constants — there is no measurement uncertainty in the multiplication, only whatever rounding the original regional definition carried. Bihar's Saran figure, 1,742.24 square feet, is quoted to two decimal places in land records; the others are round numbers by definition, so the result is exact given the figure you supply.