SYS/RES
Calculators
Value of a test, acquisition, traffic and SEO — growth arithmetic.
CPA and ROAS
Campaign spend, conversions and revenue turned into CPA, ROAS and post-acquisition margin. The three numbers that get confused once per meeting.
SYS/IN
SEA / analytics calculator — not an experiment tool. No p-value, no lift.
SYS/OUT
CPA
€62.50
CPA = spend / conversions
- ROAS
- 2.40×
- Post-acquisition margin
- €7,000.00
ROAS = revenue / spend
revenue − spend
How this is calculated
Formulas
Three identities, nothing else:
- CPA (cost per acquisition) = spend / conversions
- ROAS (return on ad spend) = revenue / spend
- Post-acquisition margin = revenue − spend
If conversions are 0, CPA is undefined (divide by zero) — the tool shows a dash, not Infinity. If spend is 0, ROAS is undefined the same way.
This is not an experiment tool. It computes neither a p-value, nor lift, nor a confidence interval. It is the SEA / analytics arithmetic that gets redone in every campaign review.
Sources
Platform definitions: Google Ads (CPA, ROAS) and Meta Ads (cost per result, ROAS). Revenue and conversions are the numbers you type in — the tool does not read an ad account.
Limits
- Platform-reported conversions are not incrementality. A €12 CPA is not proof that an ad caused €12 of cost per sale.
- No attribution window, no view-through, no VAT.
- ROAS is not margin: a 2.4× ROAS on a 20% gross-margin product can still lose money.