Most clearomizers are about the same size as regular cartomizers. There are larger ones, like the ego Vision, aka Stardust, aka CE4. The Stardust holds about 1.8ml. That's about twice the juice of a regular sized cartomizer. There are yet bigger ones, but when they get past 2ml, they're called "tanks". They work the same way, but they're just big.
Most of them are very slightly bigger in diameter than a regular cartomizer and, like cartomizers, they come in regular and XL lengths.
Many of them are finicky and need some tweaks to really work well. That put me off of them for a long time. Then, I discovered one that worked great straight out of the box and never leaks at all. It's the Fluxomizer from Gotvapes.com
I use the XL size and it holds about 1.5ml. Since there is no filler material taking up space, they hold a little more than an equvalent sized cartomizer. More importantly, they use ALL the juice. There is no left over juice like a cartomizer has when it starts to burn. You don't have to top them off. You just refill them when they're empty. And, even more more importantly, there's no filler interfering with the taste and you can refill them with a different flavor, easily clean them and they last a lot longer than a regular cartomizer. There are so many advantages to them that people were willing to tweak them to make them wick right, which was always the weak spot for the CE2 clearomizers. Now they have CE3 clearomizers with the coil at the bottom, so wicking isn't a problem.
Here is a CE2 Fluxomizer XL
Here is a bottom coil CE3 type Clearomizer
Here is a big 5ml "tank" type clearomizer