How do I determine time capsule disk capacity

The Disk capacity will appear.

Using AirPort Utility / Disk Tab, the amount of free space on the disk will appear, but the total capacity will not.....so you really don't know what the total size of the drive might be......unless you have not used any of the available space on the drive, or very little space.

In other words, my drive might read 1.4 TB Free. But, that does not tell me whether I have 1.4 TB of 2 TB free or 1.4 TB of 3 TB free.

There are other ways to find out what the total capacity of the drive might be.....if you still need that information.

There is always the option to buy the 2Tb model and amplify its capacity with a USB disk or replacing the internal disk with another. I have seen some TC up to 8TB.

http://forums.macrumors.com/threads/8tb-time-capsule-upgrade.1852486/

If you are using Time Machine to back up your Mac(s)......one easy way to check available and total disk size disk size would be to simply click on the Time Machine "clock" icon at the top of the Mac's screen, then click on Open Time Machine Preferences.

Look at the information for "Data", which is the default name of the drive on the Time Capsule....(unless, you have changed the name of the drive).

If you have a recent version of the Time Capsule......it will be either 2 or 3 TB.....not 2 or 3 GB