UOM problem

Hi friends,

  I have doubt on UOM setting.

Example process:

                 AAAA is part number . this part number purchase price is 200. i am ordering 1 roll . 1 roll= 400mtrs. my inventory uom also Mtrs

now i will go to make purchase order for 2 roll

item code   price   qty   row total

AAAA         200     2      400

after that i will go check my order qty . that should be 800 mtrs. but here conversion is not happening . my order qty also 2 nos

So what i do i change the UOM . after i create again purchase order for 2 roll

itemcode    price  qty  row total

AAAA        80000  2    160000

price is increasing it is taken like (purchase price * uom conversion (200*400)). and i check the order qty in item master data . conversion is happening correctly . but my purchase price is high . i do not how do i solve this issue . my result should be conversion and purchase price also will be correct.