Stored procedure to calculate fields and insert value

I have a question regarding creating a stored procedure to calculate a value from fields in a table using an IF statement and then insert that value to the table.  

simplified example table structure all numeric...  KEY, Weight, MinTon, BilledTon

Weight is in pounds and needs to be converted to tons in stored procedure
                                   Weight / 2000

MinTon is a numeric value of tons example= 25

  Billedton will be the inserted value of the calculation

I have played with creating a stored procedure but just can not get the syntax correct.  Here is the non working sample

 @BilledTon NUMERIC(18,0) output
 
)
AS

BEGIN

DECLARE @Weight numeric
DECLARE @MinTon numeric


Select @Weight = (Weight / 2000) From tbl_GenFrieght
Select @MinTon = MinTon From tbl_GenFrieght

WHERE LoadID = LoadID

Update tbl_GenFrieght


SET

BilledTon = Case When (@Weight < @BilledTon) Then @MinTon
             Else @Weight
         
SELECT BilledTon FROM tbl_GenFrieght

End

So the value needs to Check if Weight is less than the MinTon value  Then enter the MinTon  Value into BilledTon

Else Enter the value of Weight / 2000 into the billedton Field.

sample data:

Weight                    MinTon               Billedton
45000 (22,5)                25                        25
51000 (25.5)                25                        25.5

Thank you