Converting Bytestransferred to MB

Hi,

I am trying to create a progress bar for that shows to overall progress for a batch of mailboxes moves from Exchange 2007 to 2013.

I have managed to output the each mailbox size to a csv which I can then total.

I am trying to do the same thing with the bytestransferred value of each mailbox. I can get these values but how do I convert it MB so that it is in the same format as the mailbox size.

I have been trying to use:-

Get-Moverequeststatistics mailbox | select @{label="bytestransferred";expression={$_.BytesTransferred.Value.ToMB()}}

but it doesn't give me a value

Any ideas what I am doing wrong or how to get the values in MB instead of bytes

TIA

Andy