Speed of light =299792458m/s 0r approx 300000km/sec

Second= 9192631770 cycles of the standard caesium 133 atom(55) transition (electron vibration pulse)- in future optical clocks because of less uncertainty

Metre= the length of the path travelled by light in a vacuum during a time interval of 1/299792458 of a second

Pm=Picometer unit of length equivalent to one trillionth of a meter.

NM=nanometre unit of length equal to one billionth of a meter.

Micrometer unit of length equals one millionth of a metre.

Millimetre unit of length equals to 1000th of a metre

Centimetre unit of length is equals to 100th of a metre

Metric prefixes

Zetta meter 10^21m

Tera 10^12

Giga 10^9

Mega 10^6

Kilo 10^3

Hecto 10^2

Deca 10^1

None 10^0

Deci 10^-1

Centi 10^-2

Milli 10^-3

Micro 10^-6 – chromosome level

Nano 10^-9 – polymer of DNA level

Pico 10^-12- gamma ray wavelength level

Femtometre 10^-15-quarks

Yoctometer 10^-30

Smallest length theorised= PLANCK LENGTH = 1.6×10^-35 metres

If atom is size of earth than an proton of object in that earth would be a planck length

Last size where gravity would have an effect -size of string in string theory

Space time fabric =9.5 x 10^-36