Scale, Pivot and Axis Fixes When Importing AI Models

What the formats say

• glTF 2.0 (spec 2.0.1): right-handed, +Y up, front faces +Z, linear units in meters. A GLB from any generator that follows the spec should therefore be meters and Y-up. Whether a generator picks a sensible size for the object is a separate matter and is not defined by the spec.
• FBX: proprietary; we could not confirm its default unit or axis from a dedicated Autodesk page, so we state none.
• OBJ and STL: the Library of Congress descriptions we read do not discuss units for either format. That silence does not establish what any file contains, so treat the unit as unknown and check the scale by hand.

Per-generator default scale and axis have not been measured here. See checking raw AI 3D output for the related counts, and use the log at the bottom to build your own.

A correct unit does not mean a correct size. A GLB in meters can still contain a three-meter mug, because the spec defines what a unit means and not how big your object should be. That is why the procedure starts with a measurement instead of an import setting.

Fix in Blender

Work in Object Mode unless a step says otherwise. The order below settles size and rotation first and places the origin after them.

1. Import (importing AI 3D models into Blender). FBX has a Scale option on import; leave it alone unless you know why you are changing it, since fixing the size in the next steps is easier to reason about.
2. Measure. Check the object’s Dimensions in the sidebar against a real-world reference. The manual defines Dimensions as the size of the bounding box aligned with the object’s local axes, so on a model lying on its side the height may be listed under an axis you did not expect. Decide the true size: a mug is not three meters tall.
3. Fix the rotation. The model should stand the way it will stand in the engine. Rotate it now, before anything is applied.
4. Set the scale by scaling uniformly by the ratio of true size to measured size (worked example below). Scale the whole object; scaling one axis alone distorts the shape.
5. Apply rotation and scale. Object > Apply > Rotation & Scale (Ctrl-A). The manual says this keeps the object looking the same while resetting rotation to zero and scale to 1.0. Godot’s export page also recommends applying the object transform before export, giving 3D selection issues in the editor as its reason.
6. Set the pivot (origin) where the engine should hold the object: the bottom center for props that stand on a floor, the center of mass for things that tumble, the hinge for doors. The glTF spec does not say where an object’s origin must sit, so check where your generator puts it, or the prop may float or sink when placed.
7. Check facing. The front of the model should face the direction the engine expects. glTF’s front is +Z; Godot’s export page says that in Blender’s own axes this means -Y is the front. Rigging tools may demand a facing: Meshy’s rigging API requires the face to point +Z, per its documentation (rigging models is covered under rigging).
8. Export with File > Export > glTF 2.0 (the manual writes the path as File > Import/Export > glTF 2.0). Under Transform, Y Up exports using the glTF convention, +Y up. Under Include, choose Selected Objects or whatever scope you need. Details of formats are in GLB vs FBX vs OBJ.

A note on “All Transforms”. Many tutorials, including GamineAI’s guide and Meshy’s help article, tell you to choose All Transforms from the Ctrl-A menu. The 5.2 manual’s Apply page lists Location, Rotation, Scale and Rotation & Scale, plus All Transforms to Deltas, which is a different operation. Use whichever entry your menu shows, and be careful with Location: the manual says applying it sets the object origin to the world origin at (0, 0, 0), which undoes a pivot you placed anywhere else.

Worked example: scaling to a known size

The inputs are invented to show the arithmetic. A chair GLB imports with a Dimensions height of 3.7 m; the chair should be 0.9 m tall.

• Scale factor = true height ÷ measured height = 0.9 ÷ 3.7 = 0.243.
• Scale uniformly by 0.243, then apply Rotation & Scale. Dimensions now read 0.9 m with a scale of 1.0.

If several parts belong together, scale them as a group so their proportions and positions hold. The manual says applying transforms also applies those transformations to an object’s children.

Setting a bottom-center pivot

Set Origin (Object > Set Origin) offers Geometry to Origin, Origin to Geometry, Origin to 3D Cursor and Origin to Center of Mass. None of those means “the floor”, so use the 3D cursor:

1. In Edit Mode, select the lowest vertices or the face the prop stands on, then choose Mesh > Snap > Cursor to Selected.
2. Back in Object Mode, choose Object > Set Origin > Origin to 3D Cursor.
3. Type 0 into the object’s Location fields so the new pivot sits at the world origin.

For a tumbling prop, Origin to Center of Mass assumes uniform density, per the manual. To drag an origin by hand, enable Affect Only Origins in the Tool Settings Options.

Engine side

• Unity: FBX Model tab has Scale Factor, Convert Units, and Bake Axis Conversion. Unity’s manual says its physics system expects 1 m in the game world to be 1 unit in the imported file. GamineAI’s Blender-to-Unity guide tells readers to set Scale Factor to 0.01 for Blender models; that is one guide’s general rule, so measure your own import before copying it. Change the import setting only if you cannot fix the file. See AI 3D models in Unity.
• Godot: scene Import settings include Apply Root Scale and Root Type. Godot’s export guidance: apply transforms, triangulate, bones in rest pose, right-handed Y-up. See AI 3D models in Godot.
• Unreal: the FBX import options Convert Scene Unit and Import Uniform Scale are discussed with what could be confirmed on GLB vs FBX vs OBJ and AI 3D models in Unreal.

What goes wrong

Two more notes on units. Rigify’s manual page assumes 1 unit = 1 meter with a human about 2 units tall, and suggests scaling a differently sized character to those dimensions before positioning the meta-rig bones. And Properties > Scene > Units > Unit Scale changes only what the interface displays, according to the manual, which notes that physics simulations do not take it into account. Leave it alone when correcting an asset.

Log your own defaults

For each generator you use, record once: file format downloaded, dimensions on import in Blender, the object’s origin location, and which axis faces front. After a few assets you will know that generator’s habit and can skip the measuring.

Stop when a default cube-size reference object and your asset sit correctly next to each other in the engine, rest on the floor, and face forward.

This page is part of the Cleaning Up AI 3D Models section.