ROAS, ROI, CPA, CAC: Differences, How to Calculate and Performance Benchmarks

ROAS, ROI, CPA and CAC measure four different things — yet they keep showing up in the same meetings, swapped around as if they were synonyms. A Conversion study (2024) with 312 Brazilian e-commerce managers showed that ~41% use ROAS to decide budget without considering margin, and they are systematically investing in campaigns with an invisible loss.

The 4 metrics in one sentence each

ROAS — return on media investment

ROAS = Revenue ÷ Media spend.

Example: I spent R$ 5,000 on ads, attributed revenue R$ 22,500. ROAS = 4.5×. Looks good? It depends. ROAS does not consider product cost, shipping, fees or taxes. It is a campaign metric, not a profit metric.

ROI — return on total investment

ROI = (Revenue − Investment − Costs) ÷ Investment × 100.

With the same example: revenue R$ 22,500, spend R$ 5,000, cost of goods sold R$ 13,500 → ROI = (22,500 − 5,000 − 13,500) ÷ 5,000 × 100 = 80%.

CPA — cost per acquisition

CPA = Spend ÷ Conversions. It is the average cost to bring in a sale. With R$ 5,000 and 180 sales, CPA = R$ 27.78.

CAC — customer acquisition cost

CAC = Acquisition spend ÷ New unique customers.

Unlike CPA, which counts every sale, CAC counts every unique customer. If 180 sales came from 120 unique customers, CAC = R$ 41.67. CAC matters when you have high LTV (recurring revenue). For one-shot products, CPA is enough.

Break-even ROAS — the calculation nobody does

Benchmarks by sector in Brazilian e-commerce

Common mistakes (that still turn into budget)

• Comparing ROAS directly across sectors — a high ticket distorts it (5× in furniture can be worse than 3× in fashion).
• Ignoring attribution — organic sales attributed to ads inflate ROAS.
• Looking only at last-click — multi-touch matters in long cycles.
• Calculating CAC without deduplicating recurring customers.
• Not calculating break-even ROAS — a “healthy” campaign at 3× can be a loss if the margin is 25%.