my %MULTIPLIERS = (
    k  => 1024, 
    kb => 1024, 
    g  => 1024 * 1024 * 1024, 
    gb => 1024 * 1024 * 1024, 
);

my $num = '30k'; # or 24g or 29kb, whatever

$num =~ s/\A
        (\d+)
        ([A-Za-z]{0,2})
    \z)/$1/x;
my $key = lc $2;
$mult = exists $MULTIPLIER{$key} ? $MULTIPLIER{$key} : 1;
$num *= $mult;