As far as I know, Tierpark Berlin is the largest one (160 hectares), which is the main reason it is hard to cover the whole place in one day.
Would Whipsnade count as bigger? It's 600 acres (around 300 hectares), and it's only a "semi-safari park". As far as I know, you can bring your car, but you can also see everything but one exhibit on foot.
I was wondering just how much area the drive through at Whipsnade covers as it is a large chunk. I wouldn't be surprised if the walkaround is larger than 160 hectares, but I am looking at mainland Europe at the minute. A rough estimate using this tool shows the area I've highlighted as only 65 hectares, but then there is a lot of land that is off limits, or out of view I would guess.
Whipsnade and Port Lympne are the joint largest zoos in the UK (and I guess Europe?) at 600 acres each.
I just found a previous thread from a few years ago on the same subject after I started looking further into it Largest zoo in Europe?
My opinion (I visited just in Schönbrunn, Budapest and some of the Hungarian countryside zoos) 1. Leipzig 2. Rotterdam 3. Vienna 4. Zoo Berlin 5. Praha 6. Munich 7. Cologne 8. Pairi Daiza 9. Tierpark Berlin 10. Budapest (oh, Hungarian patriotism)
This one is almost certainly Pafos zoo. I have visited both, Pafos is far more complete, with a fantastic bird collection, albeit some poor enclosures for elephants and tigers, and just a far more complete collection. It is also significantly bigger. Doue is nice and a very pleasant visit. Some of the enclosures are so strange they are verging on questionable and that can lead to differing opinions - especially the layout and the Snow leopard, markhor and vulture exhibits have been rather divisive. Beauval's collection is much more complete in comparison, and recent developments have taken it far past Doue in my opinion. Amneville is good but not part of the EAZA due to the tiger show they put on. I've visited neither but I reckon from what I have heard that Pairi is the better zoo, especially in terms of collection. However, many of its exhibits are controversial and some are just simply awful (thinking Javan leopards etc.). Having been to Berlin zoo and Leipzig, I reckon Berlin is the better zoo. It just seems more complete. Zurich, any day imo