[francesco123]

Hello
I was wondering how much water would be needed to dissolve 4g of KCl.As to fit it in a syringe rather then IV fluid bag

[Borek]

Check the solubility (should be trivial to google) and calculate by yourself.

[Arkcon]

I don't really understand the question as asked.  Borek: has a functional answer for you, but I suspect might not like it.  So I feel we ought to work at it some more.

Hello
I was wondering how much water would be needed to dissolve 4g of KCl.

This is clear and easy to understand.  And you can look it up, and execute the procedure.

As to fit it in a syringe rather then IV fluid bag

Annnnddd, now we take two trips off the rails.  You want to make it fit in a smaller volume.  But what if the solid won't dissolve in the smaller volume?  We can dissolve things, if its soluble enough, otherwise we can't.  We can dissolve less soluble things, in more solvent (water in your case,) otherwise we can't.  We can use a better solvent, if we want less volume (although water is probably best for an ionic solid,) otherwise we can't.  Warming a solvent often helps, but if you can't warm a solvent for some reason, then we can't. 

Its just that the way you write it, it seems like you don't know these things. 

Why do you chose the vessels I.V. bag and syringe?  Do you intend to use the KCl as an injection in a living thing?  There are other problems to address, in that case.