The best way to differentiate between a loft and a studio is to understand what they really mean. A loft is an upper section of a building which is now being used as an apartment. For better understanding, consider a loft as a raised apartment or gallery inside a very big building like church, commercial building, hall, etc. A loft is a very big apartment, spacious, and there are no partitions in it.
And even without any partitions, it is spacious enough to have different areas like a sleeping area, a living room, a kitchen, and a bathroom inside the apartment. On the other hand, a studio is simply an artist's workshop and can also serve the purpose of an apartment.
A studio is usually a portion of a building, and is usually partitioned into two or three rooms at most so as to save space. In terms of size, a loft is more spacious than a studio. However, the cost of owning and maintaining a studio is cheaper compared to a loft.