Abstract It has long been known that the growth-rate of feathers of birds is limited and that long feathers take disproportionally longer to grow than small feathers, which has severe consequences on moult duration and the completeness of moult in large birds. To reveal constraints of feather growth, we present two datasets: (a) Measurements taken from 45 plucked flight-feathers (14 primaries and 31 secondaries) from 6 dead Golden Eagles (4 – 13 primaries and/or secondaries per individual); (b) Measurements taken from all primaries of six passerine species. Explanations of the variables can be found in the Excel-files. More details about the two datasets presented here and a third dataset can be found in L. Jenni, K. Ganz, P. Milanesi, R. Winkler (2020): Determinants and constraints of feather growth. Plos ONE 10.1371/journal.pone.0231925.