Iso image is bigger than original disc

[flash]

I backed up Harry Potter on to dvdr now that I have some better dvdr's
I tried making an iso image. But Instant dvd says I need a bigger dvdr.How can this be? When ripped in file mode it comes to 4,549,873,664 on disc size.And it goes on to Nero ok.
:confused:

[LIGHTNING UK!]

DVD-R/RW are only 4.37GB. An original 'pressed' DVD can be up to almost twice the size.

[flash]

No this is not the original this is one I authored my self onto dvd-r.
If I try to burn the image it's to big but in file mode it's ok.
Why should it be any bigger? I don't get it.

[LIGHTNING UK!]

DVD appends something like 300000 sectors to the beginning of the disc. This is to speed up access times and transfer rates.
Perhaps that is what's causing it?