The only difference is the arms
Minecraft has two player models. The classic model, the one Steve uses, has arms 4 pixels wide. The slim model, the one Alex uses, has arms 3 pixels wide. The head, the body and the legs are exactly the same.
The slim model appeared in 2014 together with Alex. Today the game has nine default characters, Steve, Alex, Sunny, Kai, Zuri, Efe, Makena, Ari and Noor, and each of them can be used with either model.

How the game knows which model to use
The skin file itself doesn't say which model it is for. You choose the model when you upload the skin: Classic or Slim in the Java launcher, and the arm type in the Bedrock Dressing Room.
If you pick the wrong one, the skin looks broken. A slim skin on the classic model gets a strip of black or random pixels along the arms. A classic skin on the slim model loses one column of each arm.
Which one should you choose?
- Slim arms suit thin, light characters and many girl skins.
- Classic arms suit strong characters, knights, robots and armor.
- Long sleeves and detailed cuffs are easier to draw on classic arms, because there is one more pixel of space.
- It is a question of style: there are great boy skins with slim arms and girl skins with classic ones.
How to switch a skin between Steve and Alex
Open the skin in the skin converter and choose “To slim (Alex)” or “To classic (Steve)”. The converter removes or repeats one column of pixels on each side of the arms, so the design stays the same. Then touch up small details in the skin editor.
Questions and answers
Is Alex a girl version of Steve?
Alex is a separate character with a different look. The slim model can be used for any character, not only girls.
Can I use a slim skin on the classic model?
You can, but the arms will look broken. Convert the skin first or choose the slim model when uploading.
How do I find out which model a skin uses?
Open it in our editor or viewer: the model is detected automatically from the unused pixels next to the arms.
Does the model change the hitbox?
No. Both models are the same size in the game and play exactly the same.