Believe me - they are the same. 'Bedsit' is the more usual term, and 'bedsitter' is a less common alternative. They both describe a small one-room flat where the bed (or foldaway sofa bed) is in the living area. That said, we don't tend to use either term much nowadays. Two reasons: 1. They have a rather depressing association. 2. In this globalised world, we've taken to using the more internationally recognisable word 'studio'. If you look at any property website or estate agents offering accommodation to rent or property to buy, you will never see the word 'bedsit' or 'bedsitter' nowadays. The standard term is now 'studio' or 'studio flat'.

A bedsit is like a studio flat. It is a single roomed accocmodation containing bed, cooking and living facilities: https://en.oxforddictionaries.com/definition/bedsit I have never heard of the word "bedsitter", but if you said "bedsitter" to me, I would take the meaning as someone who is staying at my bedsit and looking after it for me, whilst I was not there. Similar to the word "Housesitter" ‘Her presence means he has a house-sitter during his many forays abroad, and when he is at home he enjoys her company and finds security in it.’ https://en.oxforddictionaries.com/definition/house-sitter I may be wrong, but that is how I understand the word. I'm British by the way!

That sounds like a San Francisco or NYC thing. Also known as a shoebox ;) Thanks for throwing this term into the mix. I'd never heard it.

(US) I've also heard the word "apodment" for that type of arrangement (1 room, shared bath), if the unit is tiny and in an upscale-ish neighborhood.

Our equivalent word is single-room occupancy ( SRO ) this is a single room in a rooming house. In this setup you get a bedroom and all other rooms are shared. In an American studio apt you don't share anything, it's self-contained. I once lived in a studio, so I can attest to that term. I had to look up 'bedsit' I'd never heard that term. Note: I'm referring to American English. At any rate, we wouldn't say single-room occupancy, we'd say "he lives in a rooming house" to mean the same thing.