^^agree. My contractor knew by his experience and the direction of the joists. He confirmed it with a structural engineer, who then calculated the beams needed to carry the load.

You're a General Contractor and asking this question? Why?

I echo the above questions (and tone of disbelief) also.

There are a few things the unqualified of us can look at in order to make an educated guess, but I would strongly advise against doing anything until a structural engineer has looked at it. The quickest way the rest of us can find out is to take a sledgehammer to the wall and see if the building falls down! Load-bearing walls are more likely to be masonry rather than stud walls, but you certainly can't assume that is always the case, as some stud walls have had supports built into them. I think the only surefire way is an examination of the full length of the wall by someone who knows what he/she is looking for. Bear in mind also that some internal walls can provide lateral support to the external walls (i.e. not just loads from above).

Given the context of the question, I'll expand a little on my answer above. I assume the question is not knowing if you have one, but rather determining which ones they are.

External walls are nearly always load bearing, as they take the load of the external wall of the story above or the roof.

Joists usually run between two load-bearing walls; floorboards are laid perpendicular to the joists. Therefore a wall that is parallel to the floorboards is more likely to be load-bearing than one that is perpendicular to them. However, trimmer joists might be used for stairwell openings for example and these might not be immediately apparent without looking at the full length of the wall.

An internal wall that continues up through the next floor is bearing the load of the wall above. Though if the upper floor is a stud wall, the load will be less.

Masonry walls are more likely to be load-bearing than stud walls, but that is definitely not a hard and fast rule.

Modern roofs are generally supported by the external walls only, but that is not always the case in older houses. You'd need to check the rafters in the attic to see is anything is resting on an internal wall.

Where a house has been extended, an internal wall that used to be the external wall might still be load bearing. That is the case in our house as I can see the attic is bricked up where the house used to end.

There are probably a 101 other things to look for.

And then call a structural engineer.

Houzz doesn't have this topic addressed?!? This question has been asked many times. Do a search and there are a ton of threads that start with this question.