<P> The Celsius scale was based on 0 ° C for the freezing point of water and 100 ° C for the boiling point of water at 1 atm pressure following a change introduced in 1743 by Jean - Pierre Christin to reverse the Celsius thermometer scale ( from water boiling at 0 degrees and ice melting at 100 degrees ) . This scale is widely taught in schools today . By international agreement the unit `` degree Celsius '' and the Celsius scale are currently defined by two different temperatures : absolute zero , and the triple point of Vienna Standard Mean Ocean Water ( VSMOW ) , a specially purified water . This definition also precisely relates the Celsius scale to the Kelvin scale , which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero , the lowest temperature possible , is defined as being exactly 0 K and − 273.15 ° C. The temperature of the triple point of water is defined as exactly 273.16 K ( 0.01 ° C ; 32.02 ° F ) . </P>
the boiling point of water is 100 degrees celsius express this in si units
100 ° C