The sizes Roblox actually specifies
Roblox publishes format guidance for experience artwork, while in-game UI is responsive rather than tied to one canvas size. Separate those two jobs: export discovery artwork at a strong master size, then build the playable interface around scale, anchors and constraints.
- Experience icon: square and at least 512×512. Preview it near 150×150 because Roblox displays it at smaller sizes in parts of the site and app.
- Experience thumbnails: 16:9 and ideally 1920×1080 for high-resolution display across the Roblox site and app.
- In-game image assets: choose a source size that preserves the needed detail, then verify the result on the lowest-end device you support.
In-game UI: think in anchors, not pixels
In-game GUI should be built with Scale-based sizing and anchors, not fixed offsets. A health bar sized as {0.2, 0} scale stays 20% of the screen on a phone and on a 4K monitor; a 300px offset bar does not.
Use Scale for the responsive proportion and Offset only where a deliberate fixed adjustment is useful. Add size or aspect-ratio constraints when a control must not collapse or stretch across very different screens.
Safe areas and device cutouts
Leave the top-left corner and bottom-right corner of the screen clear: Roblox overlays its own menu button and chat toggles there. Consoles additionally reserve space for platform prompts.
Test on the smallest device you support. If your UI survives a 375px-wide phone screen with the top bar and chat visible, it survives everything.
Generating GUIs that fit these rules
If you generate your UI kit with AI, ask for it in pieces that match this list: health bar, buttons, frames as separate transparent sprites. A full-scene render has to be cut apart by hand; sprite-set outputs drop straight into ImageLabels.
GUIFoundry's GUI mode generates sprite sets with transparent backgrounds and can match a reference image's palette, so the kit you generate matches the art you already have.