Fermenter size

Just a quick question. I see a lot of guys using the glass style carboys for fermenting, these usually are 5gal I assume. Question is, for a 19litre batch is a 5gal carboy big enough to primary in? Being that 5gal is 22 litres and some change that seems to be a little tight to me ?? What you guys think?

For primary fermentation, you'll want a 6 or 6.5 gallon carboy I think. I don't think there's any downside to having too much head space... Too little gets messy.

You would be pushing the limit with a 5 gallon carboy. In my experience, you get around 5.5 gallons of liquid to full capacity in a 5G carboy.

There are 3.78L to a gallon. So...

5.5G x 3.78L = 20.79L

You would have around 1.79L of headroom to work with, so a blow off tube would be required. It can be done with a blow off. If you are in the market for a carboy, and will be consistently brewing 19L batches, I would suggest going with a larger carboy.