Or you can use a plugin that sets the scale correctly for you.
http://mosthostla.com/gamedev/bonebreaker/
And scaling in unreal is a bad idea. You want all your assets to be the exact measures they need to be with proper texel density and not what will turn surely into a mess as you progress though making your game…
eu preciso de ajuda pois estou passando por problemas quando eu importo a projeto ele vem todo desmontado e se vem montado não consigo separar alguem pode me ajudar
Não sapi se entindo perfeitamente, mas tene marcar a caixa “combine meshes”.
This helped me figure out the same problem with really small armatur compared to my mesh. My values were different is the only weird thing as setting scene scale to .1 and exporting also at .1 gave me same size. I had to scale up 100x plus in unrealthough. Not quite understanding why but your response definitly helped me thankyou!
Found solution for me. You need just renamed your Armature in blender, in something another. But don’t use word “Armature” https://www.youtube.com/watch?v=UA3rSNfn9NM
This is exactly the problem I was suffering from. Thank you for writing this solution, because after hours of trying I could not figure out what I was doing wrong. I renamed Armature and immediately got the dimensions right in Unreal Engine! 
I didn’t enjoy this solution in my case. If you rename your Armature in Blender, then Unreal will create a new root bone, which can be prejudicial if you have animations and other things that rely on the proper naming of your existing bones.
5 years later and this solved my problem, cheers! I used different decimal numbers for my scene though.