The FormID (or Form ID) of an object is the unique numerical identifier for that object, in hexadecimal. This is the 'short version' used by the engine while the game is running. Note that in the GECK, the term Form ID may be used in one of two fashions: as the Base ID of an object template, and as the Reference ID of an instanced (placed) in-game object. The Form IDs in the Object window are Base IDs. The Form IDs in the Cell View window are Reference IDs.”— Bethesda GECK glossary
A form ID is a property assigned by creators or the engine to every object in games using the Gamebryo engine (like Fallout 3, Fallout: New Vegas, and Fallout 4). This includes items, non-player characters, quests or parts of the world like a sign on a wall or the wall itself. There are two types of Form IDs: Base IDs and Reference IDs (usually shortened to Ref IDs).
A BaseID (or Base ID) is a FormID assigned automatically to an object by the GECK when a new object is created in the Object window. The Form IDs listed in the Object window are Base IDs. A Base ID is only associated with an object template in the editor, never with an instanced object in-game.”— Bethesda GECK glossary
Base ID is the number assigned to a template for an object that is used to create many instances of that object. For example all bottle caps in the game have exactly the same Base ID. This ID is used in scripts or console with commands that create new instances of object, like additem or placeatme.
The Base ID can be obtained with the G.E.C.K.. To do so, the .esm file containing the object (for base Fallout 3
Fallout3.esm, for Fallout: New Vegas
FalloutNV.esm, for Fallout 4
Fallout4.esm) must be opened in the editor and the appropriate category be selected. Expanding the "Form ID" column (between "Editor ID" and "Count") will reveal the Base ID. It is not possible to obtain the Base ID of an object ingame without using mods such as FOSE (Fallout Script Extender).
A Reference ID is a FormID assigned automatically to a Reference by the GECK when an object is placed in the Render Window. Reference IDs are required to uniquely identify each instance of an object in-game. The Form ID column of the Cell View window lists Reference IDs.”— Bethesda GECK glossary
The Reference ID is the unique ID of an individual object (unlike the Base ID, which is an ID for an object template). For example, all the bottle caps created from same Base ID will have different reference IDs. This ID is used to manipulate existing objects with commands like kill, move to, or prid, for example.
Any item that is not created by pre-defined game scripts (either original or from mods) will have reference ID starting with FF to indicate that this item belongs to this particular save game. It is for dynamically generated items, like loot from containers, random encounters or trader's wares.
Load order of modules (ESMs and ESPs) will affect the ID number of modules. The first two digits of a ID number corresponds to its load order (in hexadecimal, like the rest of the number). One must use a utility like FO3Edit to ascertain the load order of a module. Fallout3.esm's ID number is 00, as it will always be the very first module to load. The ID number series in the FF (decimal equivalent: 255) range is reserved by the game engine for objects created and saved in the gamesave file (such as PlaceAtMe'd objects, projectiles, dropped inventory, or list-spawned actors).
According to the layout of this system, the maximum number of additional modules that can be loaded by the game is 254 (256 load order ranges, - 1 for the Savegame FF range, - 1 for the always-mandatory Fallout3.esm/FalloutNV.esm).
- Editor ID
- Fallout 3 console commands
- Fallout: New Vegas console commands
- Gamebryo console commands
- Gamebryo console commands (all)
- Help:Form IDs - explanation of Form ID formatting at this wiki