Custom Metrics and Calculated Fields in Looker Studio

Why You Need Calculated Fields

Standard connectors in Looker Studio expose raw metrics — cost, clicks, sessions, conversions. But the KPIs your business actually cares about — ROAS, CPL, cart abandonment rate, revenue per session — are derived from combining those raw numbers. Calculated fields let you define those formulas once and use them across your entire report.

Creating a Calculated Field

In Looker Studio, calculated fields can be created at the data source level (available in every report that uses that source) or at the chart level (available only in that specific chart). For KPIs you use frequently, create them at the data source level.

Steps: Open your data source → click "Add a field" → name the field → enter the formula → save.

Essential Marketing Calculated Fields

• ROAS: Conversion value / Cost
• CPA (Cost per Acquisition): Cost / Conversions
• CTR: Clicks / Impressions (often already available but useful to recreate for blended sources)
• Conversion Rate: Transactions / Sessions (in GA4 connector)
• Revenue per Session: Transaction revenue / Sessions
• Cart Abandonment Rate: 1 - (Transactions / Add to carts)

Using CASE Statements

CASE statements let you create conditional categories. Example — grouping campaigns into brand vs. non-brand:

CASE
  WHEN REGEXP_MATCH(Campaign, "brand|company name") THEN "Brand"
  ELSE "Non-Brand"
END

This creates a new dimension you can use to filter or segment any chart in the report.

Common Formula Errors

Division by zero errors occur when the denominator metric has zero values for some rows. Wrap division formulas with a null check: CASE WHEN Impressions = 0 THEN 0 ELSE Clicks / Impressions END.

Type mismatch errors occur when you try to combine text and number fields. Use CAST() to convert: CAST(field_name AS NUMBER).

Our Looker Studio dashboard service includes building a complete library of calculated fields matched to your specific business KPIs. Need the underlying GA4 tracking set up correctly first? That data quality determines what calculated fields are actually reliable.