Form ID

The FormID (or Form ID) of an object is the unique numerical identifier for that object, in hexadecimal.

Overview
This is the short version used by the engine while the game is running. This identifier is assigned by the engine to every object in games using the Gamebryo engine (Fallout 3 and Fallout: New Vegas) or Creation Engine (Fallout 4 and Fallout 76). This includes items, NPCs, quests or parts of the world. Form IDs on Reference objects are referred to as Reference IDs (usually shortened to Ref IDs).

For example, all bottle caps in the game have exactly the same Form ID. This ID is used in scripts or console with commands that create new instances of object, like or.

The Form ID can be obtained with the G.E.C.K., Creation Kit, or XEdit. To do so in the G.E.C.K or Creation Kit, the .esm file containing the object (for base Fallout 3:, for Fallout: New Vegas:  , and for Fallout 4:  ) must be opened in the editor and the appropriate category is selected. In the G.E.C.K and Creation Kit, expanding the "Form ID" column (between "Editor ID" and "Count") will reveal the Form ID.

Unmodified Fallout 3 and Fallout: New Vegas do not provide functionality for easy Form ID search through the console, it is possible, however, to find out the Form ID of objects in Fallout 4 by using the Mod:Console commands (Fallout 4) console command.

Reference ID
The Reference ID is the unique ID of an individual object in the game space. For example, all the bottle caps created from the same base object Form ID will have different reference IDs. This ID is used to manipulate existing objects with commands like, , or , for example.

Any item that is not created by pre-defined game module data (either original or from mods) will have a 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
The load order of modules (ESMs and ESPs) will affect the ID number of modules. The first two digits of an 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. The load order ID of the top-level master module (such as Fallout3.esm, FalloutNV.esm, or Fallout4.esm) is always 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 dynamically created and saved in the game's save file (such as PlaceAtMe'd object, 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 dynamic FF range, - 1 for the always-mandatory top-level master ESM). Each add-on, official or otherwise requires a single module space.