2 hour layover in Madrid

Maybe, sounds tight though, but if you are willing to risk losing out on the ticket, go for it. Worse case would be needing to buy a last minute ticket for whatever flight is available. The longer time period you plan, the less the risk.

Hi from Wisconsin,
Madrid airport is the largest airport in the world. Not in passenger traffic but in acreage. If you know which gate you land at and which gate you will be departing from, then you might have an idea of how much time you would have for the 35 minute trip into Madrid and the 35 minute trip back out.

My recommendation. Don't get frustrated trying to tour Spain. Enjoy the airport. Let me give you one starting tip to enjoying it. The color wheel of elementary school. Yellow is the center of the airport. From yellow the support beams slowing morph into the ROYGBIV of childhood. If you landed at deep violet beams, then you have a good long hike to get to yellow. It is a beautiful airport.

Enjoy Portugal. We thought the food was basic but good.

wayne iNWI

When gambling on buying a separate ticket I would give myself at least 3 to 4 hours no matter the airport.

Personally, I would give myself more time. I always factor in some extra time in case my flight is be delayed for any reason. The Madrid airport is huge. Depending on the location of your gates, there may be a lot of walking and a shuttle to baggage claim. One never knows how customs and passport control will go. (Once it took over an hour to enter Canada.) But when we were there, we went thru pretty quickly. Bottom line, I would give myself at least 4 hours. Why stress yourself with a tight schedule? Better to be early at the gate for Porto. Relax and have a cup of coffee or hot chocolate and a croissant.

Have you already bought tickets to Madrid? If not, just buy to Porto. If you're starting in Porto and ending somewhere else, look at open jaw tickets (say, into Porto and out of Madrid). To find these, use the "multi city" or "multiple destinations" option on Kayak, Google Flights, airline websites, etc.

If you are already locked in to flying into Madrid and are looking to book a separate ticket from Madrid to Porto, do heed the warning about the sheer size of the airport. Be prepared for lots and lots and lots of walking, and don't hesitate to request assistance if you need it.

Also, terminals 1, 2, and 3 are connected to each other, and terminals 4 and 4S are connected to each other. But, to get between these two groups of terminals, you have to use a shuttle bus, adding further to your connection time. You also have to go through immigration, baggage claim, and customs on arrival, then recheck your bags and go through security upon departure.

So, I agree that four hours is the shortest I'd want for this "connection" on separate tickets.

We landed in Madrid and took another flight to San Sebastian on a completely different airline within two hours and it was pretty easy. It may depend on how many other flights are arriving at the same time (we arrived around 8 a.m. on a Thursday), but I think I had one person in front of me at the passport/customs control. It is a huge airport, though -- our flights were in Terminal 4 and 4S and it still takes about 30 min. to get between gates -- and that's with us fast walking. We had carry-on only, so you'd need to factor in the time to get your luggage, but the actual customs/passport wait was pretty quick. Four hours as a layover would be miserable for me, but it depends if you want to hedge your bets on whether your original flight will be delayed - we tend to plan for the norm, rather than the exception. For what it's worth, I've done carry-only except for one trip, and it's so much easier overall, esp. getting over there.