“Legroom” is the general term used in place of the more accurate “seat pitch”—which is the distance between a point on one seat and the same point on the seat in front of it. In general though, the seat pitch measurement is a good indicator of how much room your legs have between your seat and the seat in front of you.
Reviewing a list of seat pitch measurements, you’ll see the typical range is roughly 30–31 inches. Note, however, that while a higher number can mean more legroom, it’s not always a direct correlation—if the seat back is thicker, for instance, that means less legroom even if the seat pitch number might be higher.
As you might expect, legroom varies significantly between airlines and types of planes. And, of course, business and first class seats have more legroom than standard economy class seats.
On short-haul (often domestic) flights in standard seats in economy class, jetBlue and Delta Air Lines have some of the most legroom at 31-32 inches. A complete (sortable) list is here.
International flights, or “long-haul” flights, often have more legroom than domestic “short-haul” flights, though that, too, varies by airline and plane type.
SWISS, Turkish Airlines, Singapore Airlines, and Air France have some of the most legroom in economy class long-haul flights at 32 inches, and you can see a complete (sortable) list here.
Seat width is absolutely another factor determining passenger comfort, and—again—this varies between airlines and plane types.
Some of the widest seats in standard economy class long-haul flights are with Qatar Airways, Singapore Airlines, and Icelandair at 19 inches. A complete (sortable) list is here.
Bulkhead rows do have plenty of legroom, but that perk may come at a different cost. Those seats may be located near a galley or bathroom or have armrests you can’t move. What’s more, with no seat in front of you, there’s no seatback TV or space to stow a bag on the floor (all bags must go in the overhead bin during take-off and landing).
Exit row seats also generally have more legroom, though these may not recline much (or at all).
In addition to the comparison charts linked elsewhere in this article, SeatGuru has illustrated seat map layouts of each airline’s plane type. These include details about not just which seats are “good” or “bad,” but why—so you can find out whether a seat with more legroom has a downside you can live with or not.