Biggest possible double/float for a column in my MySQL database
Do not use (m,n) on the end of FLOAT or DOUBLE.  That causes a rounding (at the bottom) or a truncation (at the top).  If you want (m,n), you probably should use DECIMAL(m,n).

FLOAT stores 24 significant bits of data (equivalent to about 7 decimal digits; storage=4 bytes), with an exponent ranging over about 10 ** +/-38.

DOUBLE stores 53 bits (about 16 digits, 8 bytes) and has a huge range.

Your question is vague -- are you storing "money"?  If so, then you really should use DECIMAL(m,2).  m=8 lets you store up to a million dollars (or Euros, etc).  But m can be as big as you want.  (Remember to subtract the 2 before seeing how big the numbers can be.)  (14,2) would store up to a trillion dollars, with precision to the penny.  It will take 8 bytes of storage.