Unit Conversion

What you can convert

Length (m, cm, mm, km, in, ft, yd, mi), weight (kg, g, mg, lb, oz, ton, quintal), temperature (°C, °F, K), area (sq m, sq ft, sq yd, acre, hectare, gunta, bigha — including Indian land-area units), volume (l, ml, m³, gal, cup, oz), and speed (km/h, m/s, mph, knots, ft/s).

All conversion factors come from the NIST Special Publication 811 (the international standard reference) or the relevant ISO standards. Indian land-area conversions (gunta, bigha, acre to sq ft) use state-by-state values where they differ — Maharashtra bigha vs UP bigha for example.

The Indian land units worth memorising

Most Indian land units are defined as a fraction of the acre, which makes them exact rather than approximate. One acre is 43,560 sq ft, so a gunta (1/40 acre) is 1,089 sq ft and a cent (1/100 acre) is 435.6 sq ft. In Punjab, Haryana and Jammu & Kashmir the kanal is 1/8 acre, or 5,445 sq ft, and the marla is 1/20 of a kanal, or 272.25 sq ft. Tamil Nadu's ground is a flat 2,400 sq ft. A hectare is 10,000 sq m, which is 2.4711 acres.

The two that trip people up are the gaj and the bigha. Gaj is simply the square yard — 9 sq ft exactly — so a 200 gaj plot in Delhi or Jaipur is 1,800 sq ft. Bigha has no single definition at all: it is 27,225 sq ft in UP and Bihar, 14,400 sq ft in West Bengal, 12,000 sq ft in Madhya Pradesh and 9,070 sq ft in Punjab. A bigha quoted without a state attached is not a measurement, and any registered document will carry the area in square feet or square metres alongside it.

For money rather than land, the Indian numbering system runs on the same idea: a lakh is 100,000 and a crore is 100 lakh, or 10,000,000. So ₹1.5 crore is ₹15,000,000 and ₹75 lakh is ₹7,500,000. The number converter handles both directions along with the digit grouping (₹1,50,00,000 rather than ₹15,000,000).

Where conversions go wrong

Temperature is the one conversion that is not a simple multiplication, because the Celsius and Fahrenheit scales do not share a zero. Multiplying by 1.8 alone gives a temperature difference, not a temperature — the +32 offset is what converts the actual reading. The same applies in reverse: subtract 32 first, then scale.

Area and volume conversions are the other common trap, because the factor is squared or cubed. One metre is 3.2808 feet, but one square metre is 10.7639 square feet and one cubic metre is 35.3147 cubic feet. Using the linear factor on an area understates it by roughly a third, which on a flat purchase is a very expensive rounding error.