Best option to take a flight when I book two separate flights one domestic connecting to another international flight at EWR?

So the time gap between the domestic flight and International flight is 3 hrs.

I would only accept a transfer like that under the following conditions:

• it is a single ticket with bags checked through to the destination.
• the airport is small. Like under 10 gates and a single terminal building.

While three hours might be theoretically possible, it will only be possible if everything works perfectly. That is unlikely to happen at Newark in normal years.

If you have a single ticket your bags will be at the departing gate in 10 minutes, and you can (assuming the same terminal) walk directly there airside - no dealing with security again.

Will it be enough for me to collect the luggage and move to another terminal and complete the checking and security?

No one knows. At this point it comes down to probabilities and risk management. With 3 hours in Newark coming in domestically you have an ok chance of making it: maybe 70/30 or so. Given the consequences of missing your flight and maybe having to buy a new same day (or next ay) ticket on the spot: is that risk acceptable to you?

You can certainly increase your chances by not checking bags, and determining if you can do on-line check in for your India flight without manual doc checks (immigration, Covid, etc).

Another factor worth considering is that Newark currently has a runway replacement project in progress, extending into October, which along with weather has been regularly causing delays at the airport. That means a higher likelihood your domestic flight into Newark could be delayed, while your outbound flight to India is still more likely to leave on time.

Newark is regularly delay-plagued anyway even without construction. I wouldn't risk this, personally, certainly not with the need to claim and re-check checked bags and change terminals.

We've had plenty of similar questions on this site. "Is X amount of time enough for a self-connection in airport Y". And the answer is roughly always the same, save for a few details: it can be done, but if you don't, it will cost you.

The first point to note is that if you have checked bags, then you must take into account the check-in deadline for your second flight. This varies a lot between airlines, airports, destinations, and more. In your case, the only non-stop flights from EWR to India are flown by United or Air India, and in both cases, the check-in deadline is 60 minutes.

This means that you now have 2 hours to:

• deplane
• get to baggage claim
• reclaim your bags
• go to the departures area (which, from your question, is in a different terminal)
• queue in line and check-in

If your first flights arrives on time, this should be very easy and completely doable (compared to more complex scenarios where you need to go through passport controls for instance, or airports where inter-terminal transfers can be quite long, or if you have to wait for you luggage at CDG).

However, if anything goes wrong (flight delayed, luggage taking a bit too long to be delivered), then if you don't make it to the check-in desk for your second flight on time, you will be considered a "no show". For most fares (especially the cheaper ones), that means your booking is no longer valid, and you will have to book and pay for another flight, at the last minute. At some periods you may have an issue with availability, and nearly all time you'll have to pay a lot more for a last minute flight than one booked in advance.

Also, if this is the further flights on that ticket (e.g. you have a return flight after that), then the following flights are very likely to be cancelled as well.

With the second flight being a long-haul international flight, you have two issues which make this problematic:

• flights can be expensive
• the next flight is probably the next day, or even later.

If you have to stay overnight (most likely), then you will have to find a hotel, pay for it, along with transfers to/from the hotel, meals, etc.

If you stay overnight, you also have the issue that you may be affected by any deadlines for Covid tests and need to take a new test.

Most people say the minimum is 4 hours before two flights booked separately to have enough margin. I'd modulate that quite a bit, as it depends a lot on the combination of flights, and especially the cost and frequency of the second flight. An overnight layover is recommended in this case.

the time gap between the domestic flight and International flight is 3 hrs. Will it be enough for me to collect the luggage and move to another terminal and complete the checking and security?

Maybe, but it doesn't really matter, because the check-in deadline for the second flight will be at least 60 minutes before departure, the chance of the first flight being delayed by two hours is fairly significant, and the consequence of missing the second flight is probably even more significant. It's a risk I would not take.