While not claiming to be any authority on the bread sciences, I’d say that a roll is roughly the size of just the palm, while a bun is closer to the size of the full hand.
A bun also passes the Burger Test: Could you easily fit a burger on this bread? If yes, it’s a bun; if no, it’s a roll.
Not from the UK, but that’s a roll. If it were larger, it would be a bun, but that is most definitely a roll.
How big is a "bun" to you then? What's the cutoff?
While not claiming to be any authority on the bread sciences, I’d say that a roll is roughly the size of just the palm, while a bun is closer to the size of the full hand.
A bun also passes the Burger Test: Could you easily fit a burger on this bread? If yes, it’s a bun; if no, it’s a roll.