Unit Converter

About the Unit Converter

Convert between metric, imperial and US units for length, area, volume, weight, temperature, speed, time, data sizes, data rates, pressure, energy, power, fuel economy and angles. Type in either box and the other updates; every other unit of the same kind is listed in a table underneath, together with the formula used.

The arithmetic is exact. Each unit is stored as its legal definition (an inch is exactly 2.54 cm, a pound exactly 0.45359237 kg) and calculated with fractions instead of floating-point numbers, so 0.1 ft is exactly 0.03048 m rather than 0.030480000000000004. Results that had to be rounded are marked with ≈.

Indian units are included where they have one fixed definition: the gaj (square yard), cent and guntha for land, and the tola and quintal for weight.

Common uses

• Converting land and plot sizes between acres, hectares, square feet, square metres, gaj, cents and gunthas.
• Recipes in cups, tablespoons and fluid ounces (US, imperial or metric).
• Gold and silver weights in tolas, troy ounces and grams.
• Tyre and gauge pressure in psi, bar and kgf/cm².
• Comparing car fuel economy quoted as km/L, L/100 km or mpg.
• Checking file and storage sizes in MB, MiB, GB and GiB.
• Turning an internet plan’s Mbps into the MB/s a download manager shows.

Where the conversion factors come from

Customary units are converted using the exact definitions in NIST Handbook 44, Appendix C and the NIST Guide to the SI (SP 811); SI prefixes follow the BIPM SI Brochure. The key defining values are:

• Inch = 2.54 cm exactly, so a foot is 0.3048 m and a mile 1,609.344 m (international yard and pound, 1959).
• Pound = 0.45359237 kg exactly; an ounce is 1/16 lb and a grain 64.79891 mg.
• US gallon = 231 cubic inches = 3.785411784 L; the imperial gallon is 4.54609 L.
• Pound-force and kilogram-force use standard gravity, 9.80665 m/s²; this fixes psi and kgf/cm².
• Calorie (thermochemical) = 4.184 J; BTU (International Table) = 1,055.05585262 J; electronvolt = 1.602176634 × 10⁻¹⁹ J (exact since the 2019 SI revision).

Radians are the one exception: they involve π, so angle conversions to and from radians are rounded (shown with ≈).

Indian units: gaj, cent, guntha, tola and quintal

• Gaj — in property listings a gaj is a square yard: exactly 9 sq ft or 0.83612736 m².
• Cent — 1/100 of an acre, 435.6 sq ft, common in Kerala and Tamil Nadu.
• Guntha — 1/40 of an acre, 1,089 sq ft (33 ft × 33 ft), used in Maharashtra, Karnataka, Telangana and Gujarat.
• Tola — 180 grains, which is 11.6638038 g (3/8 of a troy ounce). Many jewellers round it to 11.66 g, so check the figure your jeweller uses.
• Quintal — the metric quintal of 100 kg, the unit in which minimum support prices for crops are announced. It is listed as 100,000 grams in the metric table of the US Metric Act of 1866 (15 U.S.C. § 205).

Bigha, biswa, kanal, marla, katha and similar land units are not included: their size changes from state to state (and sometimes district to district), so a single conversion would be wrong for many people. Use the area in square feet or square metres from your land record instead.

KB or KiB? Decimal and binary data sizes

SI prefixes always mean powers of ten: a kilobyte (kB) is 1,000 bytes, a megabyte (MB) 1,000,000 bytes and a gigabyte (GB) 10⁹ bytes. Storage makers use these.

Computers address memory in powers of two, so the IEC introduced binary prefixes in 1998: a kibibyte (KiB) is 1,024 bytes, a mebibyte (MiB) 1,048,576 bytes and a gibibyte (GiB) 1,073,741,824 bytes (NIST: prefixes for binary multiples). Some operating systems show sizes in GiB but label them “GB”, which is why a 1 TB drive appears as about 931 GB.

Network speeds are quoted in bits per second: a 100 Mbit/s (“100 Mbps”) connection moves at most 12.5 MB per second, before protocol overhead. Choose Data rate to convert between bit/s, B/s and their SI and IEC multiples.

Fuel economy: km/L, L/100 km and mpg

Indian car makers quote km/L (distance per litre); Europe uses L/100 km (fuel per distance), so the two are reciprocals: L/100 km = 100 ÷ km/L. A car that does 20 km/L uses 5 L per 100 km.

Miles per gallon depends on which gallon is meant. The US gallon (3.785 L) is about 17% smaller than the imperial gallon (4.546 L), so the same car gets a higher mpg figure in the UK than in the US. Choose mpg (US) or mpg (UK) to match the source of the figure.

Temperatures and temperature differences

The temperature formulas convert a reading on one scale to the same reading on another: °F = °C × 1.8 + 32, K = °C + 273.15. A change in temperature converts without the offset — a rise of 10 °C is a rise of 18 °F, and 1 K equals 1 °C of difference. Values below absolute zero (−273.15 °C, −459.67 °F, 0 K) are rejected because no temperature can be lower.

Limitations

• Land units that vary by region (bigha, biswa, kanal, marla, katha) are not included.
• Conversions involving radians or milliradians use π to 50 digits and are shown rounded.
• “Month” is the average Gregorian month (30.436875 days). “Year” is 365 days; the Gregorian average year (365.2425 days) is listed separately.
• Cup sizes differ: the US customary cup is 236.59 mL, US nutrition labels use 240 mL and the metric cup is 250 mL. Pick the one your recipe uses.
• Very large or very small results are shown in scientific notation. Inputs are limited to 60 characters.

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