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3DAI
Free · runs in your browser · files stay on your device

Collision Mesh Generator

What is a collision mesh? A collision mesh (or collider) is a simple, invisible shape that a game engine's physics uses instead of the detailed model, so objects can bump, stack and be hit quickly. It is usually one or a few convex hulls, boxes, spheres or capsules that hug the visible model with far fewer triangles.

Drop a model to get a convex hull under the 255-triangle limit, a compound collider of several hulls, or a box, sphere or capsule. See it over your model with its tightness, then download GLB, OBJ or FBX named for Unreal Engine (UCX_), Godot (-convcolonly) or Unity. Nothing is uploaded.

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How to generate a collision mesh online

  1. 1

    Drop your model

    Drag a .glb, .gltf, .fbx, .obj or .stl onto the tool, or try the sample chair. It is read in your browser; nothing is uploaded.

  2. 2

    Pick a collider

    One convex hull, a compound of hulls (one per mesh, or 2 to 32 clusters), or a box, sphere or capsule for the whole model or each part. Set the triangle limit per hull.

  3. 3

    Check the fit

    The colliders are drawn over the model in colour. Turn the model, the fill and the wireframe on and off, and read the hull count, triangles and tightness.

  4. 4

    Download

    Choose Unreal Engine, Godot, Unity or generic names, GLB, OBJ or FBX, and the colliders alone or with the model in one file.

Convex, compound, primitive or mesh collider?

Physics engines test simple convex shapes far faster than a detailed mesh, so most objects get one or a few of them. The more closely a collider follows the model, the more it costs. Pick the simplest one that feels right in play.

ColliderWhat it isFollows dents and holes?Physics costGood for
Primitive (box, sphere, capsule)One exact maths shape around the object or a partNoLowestCrates, balls, barrels, characters, simple props
Single convex hullThe tightest shape with no dents around the whole model, like shrink-wrapNo: it fills holes, gaps and hollowsLowRocks, bottles, props that move
Compound (several hulls)One convex hull per part or cluster, used togetherRoughly: more hulls follow the shape closerGrows with the hull countChairs, tables, vehicles, moving concave objects
Mesh (concave / trimesh)The model itself, or a lighter copy, as the colliderYes, exactlyHighest; usually static objects onlyTerrain, buildings, level geometry that never moves

Be honest with yourself about the shape: a single convex hull cannot hollow out a cup, an arch or the space under a table. Compound mode gets closer by splitting the model, but it is an approximation, not a full convex decomposition like V-HACD. For terrain and buildings that never move, use the model itself as a mesh collider in your engine. To look at a model first, open it in the 3D Model Viewer.

Need the game asset itself? Make it with AI

Turn a picture into a textured 3D model, then bring it back here for its colliders. Prefer to describe it? Make it from text. The AI tools use credits; this collision mesh generator does not.

Make it from an image →Text to 3D

More free 3D tools

3D Model ViewerGLB to FBXFBX to GLBOBJ to GLBOBJ to FBXSTL Viewer

Collision mesh generator FAQ

It is a simple shape that the physics engine uses instead of the visible model to work out hits, contacts and stacking. It is never drawn. Simple convex shapes are much faster to test than a detailed mesh, so games give each object a few boxes, capsules or convex hulls that roughly follow its outline.
A convex hull is one shape with no dents, the way plastic shrink-wrap would cover the model. It cannot follow a hollow, a hole or the gap under a table. A compound collider is several convex hulls together, for example one per leg and one for the seat, so the empty space between them stays open.
Unreal Engine reads meshes named UCX_ (convex), UBX_ (box), USP_ (sphere) or UCP_ (capsule) followed by the exact name of the mesh they belong to and a number, for example UCX_seat_00. They must be closed and convex. Pick the Unreal Engine preset and download the FBX with the model in it.
Pick the Godot preset and download the GLB. Every collider node ends in -convcolonly, so on import Godot turns it into a StaticBody3D with a convex collision shape and does not draw it. A mesh you name with -col instead gets a concave collision made from the mesh itself, which is best for static level geometry.
Import the collider file next to your model. Add a Mesh Collider to your object, set its Mesh to one of the collider meshes and tick Convex, which a Rigidbody needs. Unity limits a convex mesh collider to 255 triangles, which is the default limit here. For a compound collider, add one Mesh Collider per hull.
Because a convex shape cannot have dents. One hull around a chair also fills the space under the seat, and one around a cup fills the inside. Use Compound mode to split the model into parts, by mesh or into 2 to 32 clusters, and check the tightness: closer to 100 % means a closer fit.
No. V-HACD and CoACD split a model where it is concave, which takes much longer. Compound mode here splits by mesh or by nearby surface points (k-means clusters) and hulls each part, which is fast and works well for models built from parts. For a cave-like or very concave single mesh, more clusters help, but it stays an approximation.
It is the colliders' total volume as a share of the model's own volume. 100 % is a perfect fit; 150 % means the colliders hold half as much extra space again, for example the gap under a seat. It needs a closed (watertight) model to measure; for open models the tool shows the hull count and triangles only. Where hulls overlap, the shared space counts twice.
No. The model is read, the colliders are made and the files are written in your browser, on your device. Nothing is sent to a server.
GLB and GLTF (including Draco and meshopt compressed), FBX, OBJ (with its MTL and textures) and STL, up to 1.5 million triangles and 300 MB. Colliders come back as GLB, OBJ or FBX. KTX2 (Basis) textures are not supported yet.

Unreal Engine, Unity, Godot and Blender are named only to describe compatibility; The3DAI is not affiliated with or endorsed by Epic Games, Unity Technologies, the Godot Foundation or the Blender Foundation.