Classic vs Slim: which skin model?
Both models use a 64×64 PNG. The practical difference is the width of the character’s arms, so choose before you draw sleeve details.
The difference at a glance
4 px arms
Choose Classic for the wider default arm silhouette. The arm front and back have one extra pixel across their width.
3 px arms
Choose Slim for the narrower arm silhouette. The arm front and back have one less pixel across their width.
Choose before you export
Start in the editor or generator and select Classic or Slim.
Check both arms in the canvas and the rotating viewer. A skin can look fine on the head and still have the wrong arm proportions.
Export with the same model selected, then choose that same model in the Minecraft import screen.
Changing Classic to Slim does not resize a PNG. It changes how the arm UV regions are interpreted by the model.
Related tools
FAQ
Can a PNG tell Minecraft which model I chose?
A standard PNG does not reliably carry the model choice. Keep the model selection with your draft and choose it again when importing.
Which model should I use for a narrow character?
Use Slim. The arms are 3 pixels wide, while Classic arms are 4 pixels wide.
Is Slim lower resolution?
No. Both are 64×64; only the arm geometry differs.