Rankwise

Unit conversions

30 conversions used in physics and chemistry, each with a converter and the reason behind the number.

Updated 28 October 2026Free · no sign-up

ConversionValue
Electron volt to joule1 eV = 1.602 × 10−19 J
Joule to electron volt1 J = 6.242 × 1018 eV
Calorie to joule1 cal = 4.184 J
Kilowatt hour to joule1 kWh = 3.6 × 106 J
Erg to joule1 erg = 10−7 J
Litre atmosphere to joule1 L atm = 101.325 J
Atomic mass unit to mega electron volt1 u = 931.494 MeV
Atomic mass unit to kilogram1 u = 1.661 × 10−27 kg
Atmosphere to pascal1 atm = 101,325 Pa
Atmosphere to bar1 atm = 1.01325 bar
Atmosphere to millimetre of mercury1 atm = 760 mmHg
Bar to pascal1 bar = 100,000 Pa
Angstrom to metre1 Å = 10−10 m
Angstrom to nanometre1 Å = 0.1 nm
Nanometre to metre1 nm = 10−9 m
Fermi to metre1 fm = 10−15 m
Light year to metre1 ly = 9.461 × 1015 m
Astronomical unit to kilometre1 AU = 1.496 × 108 km
Km per hour to metre per second1 km/h = 0.277778 m/s
Metre per second to km per hour1 m/s = 3.6 km/h
Dyne to newton1 dyn = 10−5 N
Kilogram weight to newton1 kgf = 9.8 N
Horsepower to watt1 hp = 746 W
Gauss to tesla1 G = 10−4 T
Degree to radian1 ° = 0.0174533 rad
Radian to degree1 rad = 57.2958 °
Celsius to kelvinAdd 273.15 (most JEE and NEET questions use 273). A change of 1 °C is the same as a change of 1 K.
Kelvin to CelsiusSubtract 273.15. Absolute zero, 0 K, is −273.15 °C.
Celsius to FahrenheitUse C/5 = (F − 32)/9. Water freezes at 32 °F and boils at 212 °F. −40 °C is also −40 °F.
Fahrenheit to CelsiusSubtract 32, then multiply by 5/9. Body temperature 98.6 °F is 37 °C.

Two habits that save marks

  • Convert to SI first. Put every value in metres, kilograms, seconds, joules and pascals before you plug it into a formula, then convert the answer at the end.
  • Write the units through the working. If they don't cancel to the unit you expect, a conversion is missing. The dimensional formula pages help here.

Questions students ask

What is 1 eV in joules?

1 eV = 1.602 × 10⁻¹⁹ J.

What is 1 atm in pascal?

1 atm = 101 325 Pa ≈ 1.013 × 10⁵ Pa.

How do you convert km/h to m/s?

Multiply by 5/18. 36 km/h = 10 m/s.

What is 1 amu in MeV?

1 u = 931.5 MeV, from E = mc².

Use these next

Dimensional formulasDimensions and SI units of 57 physical quantities.Physical constantsValues and units of the constants used in physics and chemistry.Physics formula sheetEvery important formula, chapter by chapter, searchable.Chemistry formula sheetPhysical chemistry formulas and constants in one place.