Fish record calculator

Hi, I am trying to make a worksheet that will log the fish I catch in lbs, ozs and drams then calculate that cell as a percentage of the record fish of that species but can't even get to format a cell as weight. I'm a novice on Excel and wondered if any genius out there could do this for me. I have uploaded a .jpg of what I am trying to do for example:
B2 = 5lb 4oz 0drms
C2 = 1lb 15oz 06drms
D2 = percentage C2 is of B2
if any one could do this for me that would be greatly appreciated

Thanks The Monk