How do I find out the capacity of a DVD disc?

Disk utility should tell you this info. Are you able to select the disk in the left pane? What do you see at the bottom right? It should provide CAPACITY, AVAILABLE, USED, NUMBER OF FILES. Are these showing as blank?

Here are some capacities for you:

You can look at the surface of the blank disk for the designation of which type of disk it is (CD-R, DVD+R, etc.)

CD-R, CD-RW Capacities: 700 MB

I pulled these off Google for you.

Hope this helps 🙂

Message was edited by: Radiation Mac

For example, I am currently in the middle of erasing an old Seagate external hard drive ...

See at bottom right there are the capacity etc but you have to have the drive or partition selected on the left.

Hi,

I played with this a little in my Snow Leopard system, using both a blank CD-R disc, and also a CD-R disk that I had burned as a data CD using Finder.

I think what is happening is that when a burned CD is placed in the optical drive, it has already been formatted such that the system recognizes it as a "volume" and mounts it onto the file system the same way that it would mount a regular disk partition. Finder and Disk Utility can read the information on this mounted volume and report its capacity, free space, etc, the same way that an external disk drive would be reported. Although the icon of a burned CD appears on the Desktop, this icon does not represent a physical object in your Home/Desktop folder, but rather represents a mounted object with its "mount point" in the hidden /Volumes folder. If you Get Info on it with Finder, it will be of kind:Volume:

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By contrast, when you insert an unburned, blank CD, it has not yet been formatted and cannot be mounted in the file system. You can see an icon on the Desktop that looks like a CD volume:

However if you show all file extensions, you can see that the icon carries the extension ".fpbf" and is actually a "burn folder," not a mounted volume:

.

Such a "burn folder" is a real folder that gets created in Home/Desktop. Like any "folder", it does not have a "capacity":

So basically, Finder and Disk Utility can give volume information for burned optical media that has been formatted and mounted, but not for blank media.

If you have it, Toast gives you the information you're looking for. I put a blank CD, DVD and single layer Blu-ray disk in my drives. Press Command+I from within Toast and it gives you this type of information:

If you don't have Toast, I just looked at the free (and nice!) utility Simply Burns, and its "data burn" window also shows the type and capacity of inserted blank media.

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One viable option involves using the Terminal. Try using the command drutil:

$ drutil -drive 1 status Vendor Product Rev HL-DT-ST DVDRW GS41N UA04 Type: DVD-R Name: /dev/disk4 Write Speeds: 4x, 8x Overwritable: 510:38:38 blocks: 2297888 / 4.71GB / 4.38GiB Space Free: 510:38:38 blocks: 2297888 / 4.71GB / 4.38GiB Space Used: 00:00:00 blocks: 0 / 0.00MB / 0.00MiB Writability: appendable, blank, overwritable Book Type: DVD-R (v5) Media ID: MBI 01RG40

Excellent. Kind of amazing at times how many things you can do or find out in Terminal. But then, Unix has been around for a long time.