Event parameter limits and registration
GA4 imposes limits on events: a cap on parameters per event, and separate caps on how many custom dimensions/metrics you can register to surface those parameters in reports. An unregistered parameter is collected but not reportable as a dimension. Knowing these limits prevents the surprise of sending data that never appears. This page explains the relationship between sending, registering, and reporting parameters.
Sending vs registering vs reporting
Sending a parameter on an event is not the same as being able to report on it. GA4 limits parameters per event, and separately limits how many custom dimensions and metrics you can register per property. Only registered parameters become reportable dimensions/metrics; unregistered ones may still be collected but are not available to slice reports. The exact numeric limits are maintained in Google's documentation and can change.
Prioritising within the caps
Because registration slots are finite, decide in advance which parameters earn a slot — the ones you will actually segment by. Reserve high-value parameters for registration and let incidental ones remain unregistered or be dropped. This discipline also reduces the risk of registering near-unique, high-cardinality, or identifying values. Treat the published limits as current guidance and check them rather than asserting fixed numbers.
- Cap on parameters per event and on registered dimensions
- Only registered parameters are reportable dimensions
- Prioritise slots for parameters you will segment by
How it appears in analytics and logs
A parameter you send but cannot find as a dimension is usually unregistered, or you have hit the custom-dimension registration cap, so it never surfaces.
Diagnostic use case
Plan which parameters to send and register so the values you need actually report, staying within GA4's per-event and custom-dimension limits.
What WebmasterID can help detect
WebmasterID keeps a lean parameter model; GA4's parameter and registration caps are documented here so you prioritise the values worth reporting.
Common mistakes
- Expecting unregistered parameters to appear as dimensions.
- Burning registration slots on parameters you never segment by.
- Assuming a fixed limit instead of checking current docs.
Privacy and accuracy notes
Registration limits are a reason to be selective, which also helps privacy: register only coarse, non-identifying parameters. This is educational, not legal advice.
Related pages
- Event parameters: adding context safely
Event parameters are the key-value details attached to an event: which button, which product, which step. They are what turns a bare event name into something analysable. The craft is choosing a small, stable set of parameters with consistent names and values — and the discipline is keeping every one of them free of personal data, because parameters are stored and widely visible in tooling.
- Parameter cardinality and high-cardinality rows
Cardinality is the number of distinct values a parameter or dimension takes. When an event parameter has very high cardinality — many unique values — reports can exceed row limits and collapse the overflow into an (other) row, hiding detail. Understanding cardinality helps you design parameters that stay analysable: bucket continuous values, avoid unique-per-event strings, and reserve high-cardinality fields for where they are truly needed.
- Item-scoped event parameters
Item-scoped parameters are parameters attached to each entry inside an e-commerce event's items array — item_id, item_name, price, quantity, and custom item parameters — describing the product rather than the event as a whole. They contrast with event-scoped parameters that describe the event (currency, value, transaction_id). Knowing the scope determines where a parameter belongs and how it can be reported in GA4.
- Events reference (docs)
Keep a lean, reportable parameter set.
Sources and verification notes
- GA4 developer docs — Events (parameter limits)
- Google Analytics Help — Custom dimensions and metrics limits
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.