I'm trying to work out the formula for BLAST e value calculation. I have surfed all across the internet looking for it, but the only thing I'm able to find is the formula provided here: http://www.ncbi.nlm.nih.gov/BLAST/tutorial/Altschul-1.html The problem is, I can't get the correct value for whatever parameters I plug into it. What I do? I run blastp module of blast on a query and Uniprot database. BLAST then gives me values for gapped K and lambda, as well as scores, database length and query length. When I plug that into the formula E = K * m * n * exp (- lambda * S), I get absolute nonsense. I tried various stuff for m and n - including database length, query length, result sequence length - tried bit scores and real scores, and I simply can't get the E value which blast outputs by itself, no matter what. Is there a way to correctly calculate E value and how? Please help.

Is there some reason you need to calculate e-value for yourself? Seems like blastp has done it for you :)

Yes. I'm trying to find a way to calculate it because I need it in my project (if it is possible in any way).

Hi, did you get the answer for this questions. Thanks. If so,could you give some tips

You may see: https://bmcresnotes.biomedcentral.com/articles/10.1186/1756-0500-5-286