Coordinate systems and handedness

A coordinate system defines which direction each axis points. Two things vary between programs: which axis is up (Y or Z), and whether the axes are right-handed or left-handed. Units are the third variable; see units, scale and axes.

Handedness is easiest to check with your hands. Point your thumb along +X and your index finger along +Y; your middle finger, bent towards you, points along +Z. Whichever hand makes the picture match the program is its handedness.

#Conventions by tool

Tool or format	Up axis	Handedness	One unit	Sources
Blender	Z	Right	1 m (internal unit)	(Verge3D Wiki; Cinevva)
3ds Max	Z	Right	Inches by default (system unit)	(Verge3D Wiki; 3ds Max 2016 Help)
Maya	Y by default, can be set to Z	Right	Centimetres by default	(Verge3D Wiki; Maya 2024 Help)
Houdini	Y	Right	Not stated in the source used	(Houdini Engine for Unreal documentation)
Unreal Engine	Z, with X forward	Left	1 cm	(Unreal Engine 5.8 Documentation; Unreal Engine 5.8 Documentation)
Unity	Y	Left	1 m	(Unity 2022.3 Manual; Unity 6.6 Manual)
Godot	Y	Right	1 m	(Godot Engine 4.5 Documentation)
glTF 2.0	+Y; the front of an asset faces +Z	Right	Metres	(Khronos Group)
USD	Y or Z, stored per stage as `upAxis`; fallback Y	—	—	(OpenUSD API documentation)

A two by two grid of axis gizmos. Top row Y-up, bottom row Z-up; left column right-handed, right column left-handed. Each gizmo shows three labelled arrows with the up axis in orange, and the tools that use it listed underneath. Y-up right-handed: Maya, Houdini, Godot, glTF. Y-up left-handed: Unity. Z-up right-handed: Blender, 3ds Max. Z-up left-handed: Unreal Engine. — The four combinations of up axis and handedness, and which common tools use each. An asset moving between any two boxes needs a conversion.Diagram by the handbook author

#Axis conversion between tools

An exporter or importer has to swap axes, and sometimes flip one, to keep the asset looking the same. SideFX's Houdini Engine documentation gives a worked example: Houdini is "a Y-up right handed coordinate system, while Unreal uses a Z-up left handed coordinate system", so "an asset located at (0, 10, 5) in Houdini will be located at (0, 5, 10) in Unreal" (Houdini Engine for Unreal documentation: Coordinate System). Y and Z swap; the object stays in the same visual place.

The same documentation notes a limitation: only recognised vectors are converted, so "a single "Y Position" parameter exposed in Houdini will actually control the Z position in Unreal's coordinate system" (Houdini Engine for Unreal documentation: Coordinate System). Conversion applies to geometry, but not necessarily to every number attached to it.

#Other effects of handedness

Normal maps have their own handedness: the OpenGL (Y+) and DirectX (Y−) green-channel conventions. See tangent space and MikkTSpace and normal map.
Mirroring with negative scale flips winding order, which glTF accounts for explicitly (Khronos Group: glTF 2.0 Specification).
USD assets may disagree with each other. OpenUSD stores the up axis per stage, with legal values "Y" and "Z", and suggests that a "conscientious set/environment-construction tool could examine the up axis of referenced assets" (OpenUSD API documentation: Encoding Stage UpAxis). See USD for environment artists.

#Common mistakes

Rotating in the engine to hide an export problem. The next re-import brings the problem back.
Testing only a single cube. Axis bugs often appear only with children or animation (Unity Discussions: "Bake Axis Conversion" import setting).
Assuming "Y-up" means the same thing everywhere. Unity and Godot are both Y-up and metric, but differ in handedness (Unity 2022.3 Manual: Rotation and orientation in Unity; Godot Engine 4.5 Documentation: Introduction to 3D).

#Further reading and watching

Coordinate Systems (Verge3D Wiki)

a short comparison of up axes and handedness across Blender, 3ds Max, Maya and engines. Beginner, free.

WebBeginnerFree

Coordinate System (Houdini Engine for Unreal)

a worked example of converting Y-up right-handed to Z-up left-handed. Intermediate, free.

DocsIntermediateFree

Coordinate System and Spaces in Unreal Engine (Epic)

Unreal's axes and its world, local and other spaces. Beginner, free.

DocsBeginnerFree

FBX rotation fix for Unity (KatsBits)

the classic Blender-to-Unity rotation fix. Beginner, free.

WebBeginnerFree

References

Soft8Soft · Coordinate Systems · Verge3D Wiki, 2026 · docs · accessed 2026-10-21

Cinevva · Blender to Unreal Engine Export Checklist: FBX Settings, Bone Axes, and Scale (2026) · Cinevva, 2026 · article · accessed 2026-10-20

Autodesk · Units Setup Dialog · 3ds Max 2016 Help, 2016 · docs · accessed 2026-10-20

Autodesk · Settings preferences · Maya 2024 Help, 2024 · docs · accessed 2026-10-20

SideFX · Coordinate System (Houdini Engine for Unreal) · Houdini Engine for Unreal documentation · docs · accessed 2026-10-21

Epic Games · Coordinate System and Spaces in Unreal Engine · Unreal Engine 5.8 Documentation, 2026 · docs · accessed 2026-10-20

Epic Games · Units of Measurement in Unreal Engine · Unreal Engine 5.8 Documentation, 2026 · docs · accessed 2026-10-20

Unity Technologies · Rotation and orientation in Unity · Unity 2022.3 Manual, 2022 · docs · accessed 2026-10-20

Unity Technologies · Preparing your model files for export · Unity 6.6 Manual, 2026 · docs · accessed 2026-10-20

Godot Engine contributors · Introduction to 3D · Godot Engine 4.5 Documentation, 2025 · docs · accessed 2026-10-20

Khronos Group · glTF 2.0 Specification · Khronos Group (GitHub) · docs · accessed 2026-10-21

Pixar Animation Studios · Encoding Stage UpAxis · OpenUSD API documentation, 2026 · docs · accessed 2026-10-21

KatsBits · FBX rotation fix for Unity · KatsBits Blender Knowledgebase, 2023 · article · accessed 2026-10-20

Unity Technologies · Model tab (FBX Importer) · Unity 2022.3 Manual, 2022 · docs · accessed 2026-10-20

Unity Discussions forum members · "Bake Axis Conversion" import setting · Unity Discussions, 2020 · forum · accessed 2026-10-20