Theory:

Metric units of length (mm, cm, m, km)
Converting large units to smaller units.
\(1 \ cm = 10 \ mm\)
\(1 \ m = 100 \ cm\)
\(1 \ m = 1000 \ mm\)
\(1 \ km = 1000 \ m\)
 
Converting smaller units to larger units.
\(1 \ mm = 1/10 \ cm\)
\(1 \ cm = 1/100 \ m\)
\(1 \ m = 1/1000 \ km\)
Metric units of length (kg, g)
Converting kilograms (\(kg\)) to grams (\(g\)).
\(1 \ kg =1000 \ gm\)
 
Converting grams (\(g\)) to kilograms (\(kg\)).
\(1 \ gm = 1/1000 \ kg\)
Metric units of length (lt, ml)
Converting litres (\(lt\)) to millilitres (\(ml\)).
\(1 \ lt = 1000 \ ml\)
 
Converting millilitres to litres
\(1 \ ml =1/1000 \ lt\)