Thought I knew how to do this, but not even sure which function I now need!

I have two worksheets.
INPUT SHEET
A list which basically has fields Product Description, Group Code and Tonnage.
e.g. Wheatfeed, WH, 10.00
OUTPUT SHEET
Is a form which we have to send off summarising our business activity based
on the INPUT SHEET.
Simply put it has the fields Group Code, Group Description and Total Tonnage.
e.g. WH, Wheat Products, 500.00

Its the Total Tonnage column in which I want to put formula into which looks
in the Input Sheet and totals up all the products which have the same code as
listed in the first column of the Output Sheet e.g. WH.

Any ideas???!