[ QUOTE ]
Depends on how what....what kind os surface...wether the runway is grooced, etc.
There really isn't one rule of thumb that I have ever heard.
[/ QUOTE ]
150,
It varies with what cime said here, along with aircraft type, drag devices available, etc, etc. So you'd need to work the performance charts for these problems, since there's really no one rule-of-thumb that applies, though it'd be nice to have one.