How to calculate Blocksize for cdrecord?

Hi, I went through 3 dual layer DVDs last night trying to figure this out. When using DL discs with cdrecord, you have to specify the layerbreak size. After 2 failed burns, I finally saw that the blocksize was 2048*2038 (4173824 blocks), and I was able to specify the correct size. My question is, how do you calculate the blocksize?
According to the cdrecord manpage:

 

Well, I still haven't been able to find an answer, but I found a crude work around. Just before burning begins, it shows the blocksize, and you can type ^C to quit the program before burning starts. I then take that number and divide by 2, and use that in the layerbreak= option, and it works perfectly.
The problem is, if you don't specify a correct blocksize, cdrecord will fill up the entire dual layer disc with pad data, though it wont actually write the data track.

 

On Debian, I have used growisofs to write DVDs, and I don't recall having to calculate a blocksize. There isn't cdrecord in Debian any more, there is a Debian fork called wodim. I can't remember for sure but I am guessing that wodim doesn't support DVD, otherwise I wouldn't have installed growisofs.

 

Thanks for the suggestion, but I prefer to use cdrecord over wodim.