Search Multiple and Calculate Depending on Find. plz help!

I can't seem to figure out, or find the solution:

I'd like to search a cell, D6, and depending on which match is made, a specific calculation done in the target cell.

So I know this function:

=IF(ISNUMBER(SEARCH("oz",D6)),(C6*28),"")

Which works great, but I would like it to continue:

if oz then D6*28, if lb then D6*454, if lbs then D6*454, if g then "" do nothing.

Please help !!
Thanks for the assistance !