How To Create Character Count Function

Hello Friends,

I need your help...!

i want to create one function...!

if string has total Character's '160' [/b ]or 'Less' then 160 ? I'll get just [b]'1' in result...!

if string Character limit 'double' (160+160) = 320? But not Less then 160? I'll get '2' in result...!
same triple limit 640 not Less then 320. so I'll get '3' in result.

Please explain logic with code..

Thanks