How much space is needed on a 2003 server that's being migrated to SBS2011

I have a customer who has an SBS2003 server.  It's 6yrs old and out of data space on the OS drive (has 2.5%).

How much do I need to free up prior to the migration?  I think MS says it want 10% but can't seem to find it.
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Olaf De CeusterCommented:
Hi Creativenetworks,
I can't find a precise figure. I have migrated one server with only 6% free space without issues.
The BPA flaged the lack of space but Migration preparation tools didn't flag anything.
Not an answer just a real life example.
Hope that helps,

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