Quantity conversions using customer exit.

Dear SDN,

I have created a Query to display the Sales Qty Actual vs Plan.

I am getting the values in different dimensions NM3,M3,GLL...I want to display the Query output in Metric Tons.

In which user exit I have to write the code?

Please provide the code to convert from NM3,M3,GLL..etc to Metric Ton.

Thanks & Regards,

Praveen.K