TL;DR
Revit has four kinds of parameters, defined by where they live: family parameters (inside one family, formula-capable, not taggable), shared parameters (defined in an external file, reusable everywhere, taggable and consistently schedulable), project parameters (attached to categories in one project), and global parameters (project-wide values that drive dimensions). Pick by asking two questions: does the value need to appear in a tag, and does it need to exist across families or projects?
Key Takeaways
- ✓Four kinds, defined by scope: family, shared, project, and global parameters.
- ✓Family parameters power formulas inside a family but can never appear in tags.
- ✓Shared parameters are the only custom parameters tags can display — define once, reuse everywhere.
- ✓Project parameters bolt data onto whole categories within a single project.
- ✓Global parameters are project-wide drivers — one value controlling many dimensions.
- ✓Every parameter also carries a data type and (in families) a type/instance scope — three separate decisions.
“Parameter” is one word in Revit for four different mechanisms, and choosing the wrong one is invisible until it hurts — a tag that refuses to read a value, a schedule with three columns holding the same data under different names, a “standard” height that had to be changed in ninety places. Here is the map.
The Four Kinds at a Glance
| Kind | Lives | Taggable | Best for |
|---|---|---|---|
| Family | Inside one family | No | Driving geometry with formulas |
| Shared | External .txt file, used anywhere | Yes | Data that tags and schedules must read consistently |
| Project | One project, per category | No | Project-specific data on whole categories |
| Global | One project, project-wide | No | Standard values driving many dimensions |
Family Parameters — The Workhorses
Created in the Family Editor, family parameters drive geometry: labeled dimensions, visibility toggles, material slots, and every formula in the family. This is where the whole formula system operates — from arithmetic to lookup tables. Their limitation is reach: the data is invisible to tags, and two families with a same-named family parameter still count as two unrelated parameters in a schedule.
Shared Parameters — The Data Backbone
A shared parameter is defined once in an external .txt file with a unique ID, then loaded into any family or project. Because Revit knows “Fire_Rating” here and “Fire_Rating” there are the same parameter, it can tag it and schedule it across categories consistently. The rule that catches everyone: if a value ever needs to appear in a tag, it must be a shared parameter — family parameters never qualify. Office practice: one shared parameter file for the whole company, treated like a standard, never forked.
Project Parameters — Category-Wide Bolt-Ons
Created in Manage → Project Parameters, these attach a field to every element of chosen categories in one project — “Handover_Status” on all doors and windows, a QA checkbox on all equipment. Built on a shared parameter definition they become taggable; built ad hoc they stay schedule-only.
Global Parameters — Project-Wide Drivers
Global parameters (Manage → Global Parameters) hold project-wide values that can drive dimensions and element properties directly: set Std_Mounting_Height = 1050mm once, assign it to ninety dimensions, and the next design change is one edit. Think of them as the project-level version of what formulas do inside a family.
Two More Decisions Every Parameter Needs
Data type — Length, Number, Integer, Angle, Yes/No, Text, Material, and more. The type decides what formulas can do with it: lengths carry units into the math, Yes/No values power visibility automation, text selects label phrases.
Type vs instance scope — does changing the value affect every copy or just one? This deserves its own decision test: the scope of control chapter covers it, including the rule that type-parameter formulas cannot reference instance parameters.
The Decision Flow
Key Takeaways
- ✓Drives geometry inside one family → family parameter.
- ✓Must appear in tags, or must mean the same thing across families → shared parameter.
- ✓Project-specific data across whole categories → project parameter (on a shared definition if tagged).
- ✓One standard value driving many dimensions in a project → global parameter.
- ✓Then choose the data type, then choose type or instance scope.
Frequently Asked Questions
Put parameters to work
Parameters are the nouns — formulas are the verbs
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