This formula library covers common marketing KPIs and the assumptions behind them. Formulas are useful only when the numerator, denominator, time period, and attribution source are consistent.
Quick Reference
| KPI | Formula | Important note |
|---|---|---|
| CTR | Clicks / impressions x 100 | Compare by channel and intent. |
| CPC | Cost / clicks | Average paid per click. |
| CPM | Cost / impressions x 1,000 | Useful for impression-based buying. |
| Conversion rate | Conversions / interactions x 100 | Define what counts as a conversion. |
| CPA | Cost / conversions | Can mean lead, sale, signup, or other action. |
| ROAS | Attributed revenue / ad spend | Revenue metric, not profit by itself. |
| ROI | Return or profit / investment cost x 100 | Use a clearly defined cost scope. |
| Break-even ROAS | 1 / gross margin | Simplified margin-based floor. |
| AOV | Revenue / orders | Order value, not customer lifetime value. |
| CAC | Acquisition-related costs / new customers | Cost scope matters. |
| LTV | Average purchase value x purchase frequency x lifespan | Simple revenue model used by the QMT LTV Calculator. |
| LTV:CAC | LTV / CAC | Interpret with margin and payback. |
| Customer churn | Customers lost / starting customers x 100 | Do not mix with revenue churn. |
| Profit margin | Profit / revenue x 100 | Define gross, operating, or net profit. |
Formula Caveats
- CAC is broader than platform CPA when sales, tools, salaries, or agency costs are included.
- LTV can be revenue-based, margin-adjusted, cohort-based, or churn-based.
- ROAS can look strong while ROI is weak if margin and fulfillment costs are ignored.
- Churn needs a period: monthly churn and annual churn are not interchangeable.
- Benchmarks should be used only after the formula and data source match.
For practical calculation, use the Marketing KPI Dashboard, ROAS Calculator, CAC Calculator, and LTV Calculator.
Sources and Methodology
The formulas here are definitions or arithmetic relationships. Where platform terms are used, official Google definitions are preferred. Where multiple business definitions exist, the article labels the model instead of claiming one universal formula.
