Two seats in the same economy cabin can offer noticeably different legroom. The variation is a consequence of fixed points inside the fuselage that the seat plan has to work around.
Pitch measures spacing, not space
Seat pitch is the distance from one point on a seat to the same point on the seat ahead. It describes how the rows are spaced along the floor track.
Actual room for a person's legs depends additionally on how thick the seat back is and where the underseat structure sits. Two cabins at identical pitch can feel different.
This is why comparing pitch figures across airlines is only a rough guide. It captures the geometry of the installation rather than the experience of sitting in it.
Exit rows dictate their neighbours
Certification requires a clear path to each overwing exit, so the row beside it must be spaced to leave that path unobstructed. The result is generous legroom.
The row immediately ahead of an exit often cannot recline, because a reclined seat back would narrow the escape route when it is most needed.
So an exit pair produces one row with unusual space and one with a restriction, and both are priced accordingly rather than sold as ordinary seats.
Galleys and lavatories anchor the layout
Kitchens and toilets attach to plumbing, power and structural hardpoints that cannot be moved without significant engineering. They are effectively fixed before any seat is placed.
Rows adjacent to those modules have to fit the gap that remains, which can be slightly larger or slightly smaller than the standard interval used elsewhere.
The last row before a rear galley is the familiar case: often unable to recline, sometimes narrower where the fuselage tapers, and frequently the noisiest position in the cabin.
Bulkheads create a different trade
A bulkhead row has no seat in front, which removes the reclining passenger but also removes the space beneath that seat where a bag would normally go.
Tray tables must then fold out of the armrest, which narrows the seat itself slightly. The extra floor space is real, but it comes with compromises.
Bulkheads are also where bassinet fittings are installed on longer routes, so the row's character depends heavily on who is assigned to it.
Why the same aircraft type differs between airlines
Cabin layout is chosen by the operator, not the manufacturer. An airline decides how many seats to fit within the certified limits and the available exits.
Adding a row means reducing pitch across the whole cabin by a small amount, a change most passengers cannot detect individually but which alters the economics of every flight.
That is why two carriers flying the same model can offer visibly different cabins, and why the seat map matters more than the aircraft type printed on the booking.