I prefer rounding to the nearest K, as in:

my $k_size = sprintf "%.0fK", $size / 1024;
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Or perhaps always rounding up, so that we never show a small file as "0K", which seems intuitively to mean an "empty file" for me:

my $k_size = sprintf "%dK", ($size + 1023) / 1024;
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-- Randal L. Schwartz, Perl hacker