Is this seat taken?
A very common alternative, literally meaning 'Is it free?'. Use it interchangeably with '¿Está ocupado?'.
Means 'Is there someone here?'. A slightly more indirect way to ask if the seat is available.
A more formal and complete sentence. It means 'Excuse me, is this seat taken?' and is great for being extra polite.
A direct and polite request: 'Can I sit here?'. It shifts the focus from the seat's status to your action.
Excuse me, is the seat next to the window taken?
Hi, is this chair free?
Pardon me, is anyone here or can I sit down?
On the bus: Sir, is this (seat) taken?
The phrases '¿Está ocupado?' and '¿Está libre?' are universally understood and are the most common ways to ask.
The standard phrases are used. You may also hear '¿Está ocupado este lugar?' where 'lugar' means 'spot' or 'place'.
It's very common to add a politeness marker like 'Qué pena' or 'Disculpe' before the question, e.g., 'Qué pena, ¿está ocupado?'.
The phrases are the same, but in very informal contexts, 'Che' might be used at the beginning: 'Che, ¿está ocupado?'.
The phrases '¿Está ocupado?' and '¿Está libre?' are also standard in Spain. There are no significant differences for this particular phrase.
Saying '¿Es ocupado?' — This is incorrect. You must use the verb 'estar' ('está'), not 'ser' ('es'). A seat being taken is a temporary state, not a permanent characteristic, and 'estar' is used for temporary states and locations.
Translating literally to '¿Es este asiento tomado?' — The word 'tomado' means 'taken', but in Spanish, it's not used for seats. It can mean 'grabbed' or even 'drunk'. The correct adjective for an occupied seat is 'ocupado'.
Using the wrong gender, like '¿Está ocupada?' for 'el asiento'. — In Spanish, adjectives must match the gender of the noun. 'El asiento' (seat) and 'el lugar' (place) are masculine, so you must use 'ocupado'. If you are asking about 'la silla' (the chair), which is feminine, then you would correctly use 'ocupada'.