Hány, mennyi

 

Q: What is the difference between mennyi and hány?

(answers copied from jsiehler and vvsey) 
https://forum.duolingo.com/comment/16692481 = https://archive.ph/HN5vv

Basically, "uncountable versus countable." Usually, hány is translated as "how many" and is asking about something you can answer by counting (discrete units). Mennyi is "how much" and is asking about a quantity that is not necessarily countable.

How many apples are in the basket? Hány alma van a kosárban?

How much water is in the tub? Mennyi víz van a kádban?

But Hungarian is more forgiving here, you can use "mennyi" with countable objects, as well. Not the other way around, though. Let's say it depends on whether you expect a "countable answer".

Q: Mennyi alma? - A: Két kiló (Two kilos). Or you can say the number of apples.

Q: Hány alma? - A: Tizenöt (15). I was definitely asking the number of apples.

And "Mennyi" can also be used in exclamations like "Wow, look at all those cars!" - "Mennyi autó!" In this case, the countability does not matter at all. You use "mennyi".

You can also ask: Mennyi fa van az erdőben? (How many trees are in the forest?)

How about annyi and ahány?

The same countable- uncountable distinction is carried over:

(amennyi - uncountable)

• Annyi víz van a folyóban, amennyi a tengerben.

• There is as much water in the river as in the sea.

(ahány - countable)

• Annyi póló van a szekrényben, ahány ing.

• There are as many T-shirts in the wardrobe as there are shirts.

Like before, amennyi might be used for countable things too.

See also:  Frequently asked questions