How big is a blue whales fin at birth and an adult?

It's hard to give an exact size for a blue whale's fin at birth and as an adult because:

* Fin size varies: There's natural variation in fin size even among blue whales of the same age.

* Growth is uneven: Fins don't grow at the same rate as other body parts.

However, here's a general idea:

* Birth: A newborn blue whale is about 20-25 feet long and weighs around 3 tons. Their flippers are proportionally larger compared to their body size than adult whales. We don't have specific measurements for newborn fin size.

* Adult: Adult blue whales can grow up to 100 feet long and weigh up to 200 tons. Their pectoral fins (the ones on their sides) can be up to 15 feet long.

So, while we don't have specific measurements for the newborn fin, you can imagine it being quite small compared to the adult's 15-foot-long fin!