When manually fixing an OBJ 3D model’s scale, wrong sizing often comes from OBJ files lacking embedded unit information—your software uses a default unit (e.g., meters vs. millimeters) that conflicts with the model’s original context.
OBJ relies on external unit settings (from the exporter or importer) instead of storing them. So adjusting scale without matching the original unit to your software’s default will make the model too big or small.
To fix this, confirm the model’s original unit (e.g., from its source) and set your software to the same unit before scaling—this removes guesswork and keeps dimensions accurate.