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TL;DRLikes, comments and reach don't pay the bills. ROAS, CPA and CAC do. ROAS tells you how much revenue every euro of ad spend brings back. CPA is what one action (a purchase, a lead) costs you. CAC is the total cost to acquire an actual customer, across all channels. If you don't track these three, you're running ads on hope. This guide breaks them down with real examples.
Why do ads get thousands of likes, hundreds of comments, and yet sales don't move? Because likes are vanity, and vanity doesn't pay for inventory. The three metrics that tell you if paid advertising actually makes money are ROAS, CPA and CAC. Miss them, and you're optimizing for the wrong thing.
Below is a practical guide, with real examples, on what each one measures, how to calculate it, and how to read it without fooling yourself.
ROAS — Return On Ad Spend
ROAS tells you how much revenue you get for every euro spent on ads. Formula:
ROAS = Revenue from ads ÷ Ad spend
Example: you spend €1,000 on Meta Ads and generate €3,000 in sales attributed to those ads. ROAS = 3.0, meaning €3 back for every €1 spent. Sounds great, right? It depends. ROAS ignores your product cost, your fulfillment cost, your overheads and your VAT. A ROAS of 3.0 on a product with 20% margin is losing money.
Rules of thumb:
- ROAS 1.0 = break-even on ad spend only. You're still losing on product cost, fulfillment, salaries.
- ROAS 2.5-3.5 = typical minimum for a healthy e-commerce brand with 30-45% product margin.
- ROAS 5.0+ = strong performance, usually with high margin, brand equity, or repeat customers.
ROAS is useful, but on its own it can lie. Which is why you also need CPA.
CPA — Cost Per Acquisition
CPA is what one action costs you: a purchase, a lead, a signup, a booking. Formula:
CPA = Ad spend ÷ Number of actions
Example: you spend €1,000 on Meta Ads and get 40 purchases. CPA = €25 per purchase. If your product sells for €100 with 40% margin (€40 gross profit per unit), you're profitable on ads (€40 profit minus €25 CPA = €15 net per sale). If it sells for €30 with 50% margin (€15 gross), you're losing €10 per sale.
CPA is the metric that tells you if the math works on a per-unit basis, regardless of your revenue mix.
CAC — Customer Acquisition Cost
CAC is the total cost to acquire a new customer, across every channel and every effort. Formula:
CAC = Total marketing + sales spend ÷ New customers acquired
Example: in a month you spend €5,000 on Meta Ads, €2,000 on Google Ads, €1,500 on SEO retainer, €1,000 on email tools, and you acquire 100 new customers. CAC = €9,500 ÷ 100 = €95 per customer.
Why CAC matters more than CPA over time: CAC accounts for everything you're actually spending to grow, not just the ad-spend line. If your CPA on Meta is €25 but your CAC is €95, it's because you have costs Meta doesn't see (SEO, tools, team, email).
CAC only makes sense when compared to LTV (Lifetime Value) — how much a customer is worth to you over their entire relationship. Rule of thumb: LTV:CAC ratio should be 3:1 or better. If a customer is worth €300 over 2 years and CAC is €100, you're at 3:1. If CAC is €150, you're under-earning.
Which one should you track?
All three, in different windows.
| Metric | Time frame | Decision it drives |
|---|---|---|
| ROAS | Daily / weekly | Which ad set gets more budget, which one gets killed. |
| CPA | Weekly / monthly | Whether a channel or campaign type is profitable per unit. |
| CAC | Monthly / quarterly | Whether the entire marketing operation is sustainable long term. |
Common mistakes when reading these metrics
Meta and Google report ROAS based on their own attribution windows and models. Real revenue rarely matches. Always cross-check with your Shopify / GA4 order data.
Revenue reported by Meta is usually gross of VAT. If VAT is 19-25%, your real ROAS is 15-20% lower than what you see. Always calculate on net revenue.
Ad platforms only see their own CPA (cost per action within that platform). CAC is the total, across every channel. Don't confuse them, they lead to opposite conclusions.
A tiny campaign with ROAS 8 doesn't beat a larger campaign with ROAS 3 that brings 10x the volume. Volume matters. Aim for the highest ROAS you can hit at the volume you need.
If a customer buys once and never again, LTV = one order. If they buy twice a year for 3 years, LTV = 6 orders. Your acceptable CAC can be much higher on repeat-purchase products.
How we help at ALLSoft Agency
At ALLSoft Agency, we track all three, not just the flattering one. Every client gets a monthly report with ROAS (in-platform vs. real Shopify / GA4), CPA per channel, and blended CAC. We're the ones who tell you honestly if a channel that looks profitable in Meta's dashboard is actually losing money once you back out VAT and fulfillment.
- Full server-side tracking so Meta Ads, Google Ads and TikTok all see the same real numbers.
- Cross-channel blended CAC calculated monthly against LTV.
- Written monthly reports that don't hide behind vanity metrics.
Free 24h audit. We calculate real ROAS, CPA and blended CAC against your Shopify / GA4 data, and tell you where the money is actually going. Write to info@allsoftagency.ro or call +40 756 247 611.
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