FAQ
Java: Size Limit
General information: Java block and item models can only contain elements between -16 and 32 in the edit mode (=3 blocks ingame). They are limited to this size by Minecraft itself!
Item models can be displayed larger via display mode (top right option) and using the scale sliders in the relevant displays to resize the model.
Maximum size in ingame blocks for the different slots (when the model is 3x3x3 blocks big in edit mode and scale is set to 4) for a player (or play-like entity):
Slot | Size | Base Size Multiplier
───────────┼──────┼─────────────────────
Head | 7.5 | 0.625
Hand | 12.0 | 1.000
Item frame | 6.0 | 0.500
(Formula = 3 x 4 x base_size_multiplier)
Keep in mind that a model stops rendering with the entity holding/wearing it. An entity stops rendering once its hitbox is not in your point of view anymore.
1.19.4 and newer: Item displays
If you wanna have models that are placed in your world (so not in an entity's hands etc.) you can use item_display entities.
Item_display entities have no scale limit and render even if the entity is not in your POV (unless actively specified otherwise).
/summon item_display ~ ~ ~ {transformation:{left_rotation:[0f,0f,0f,1f],right_rotation:[0f,0f,0f,1f],translation:[0f,0f,0f],scale:[2f,2f,2f]},item:{id:"minecraft:stick",Count:1b,tag:{CustomModelData:1}}}
This would summon an item_display entity using the CustomModelData:1 model of a stick, and display it twice as large than it is in Blockbench's Edit Mode.
PS: You don't need to use CustomModelData if you don't want to, this is just an example. There is also a lot more settings this entity can have (render distance, shadow, brightness etc.). More information about the entity can be found in https://minecraft.fandom.com/wiki/Display#Entity_data or in generator websites like https://mcstacker.net/ .
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