Many advertisers look at ROAS (revenue / ad spend) and stop there. But a 3.0 ROAS can still lose money on thin margins — real ROI measurement goes deeper.
The base formula: ROI = (gross profit from ad-driven orders − ad spend) / ad spend. Gross profit must subtract product cost, shipping, marketplace fees, and the return rate. For example, a 3.0 ROAS at a 40% gross margin yields only about 20% actual ROI.
Break-even ROAS = 1 / gross margin. A 40% margin needs at least 2.5 ROAS; a 25% margin needs 4.0. Compute this before launching so you know your kill threshold.
Don't ignore long-term value: if customers return for a 2nd–3rd purchase, lifetime value (LTV) justifies paying more than single-order break-even for first acquisition. Shops with a 30%+ repeat rate can break even on the first order and still profit overall.
On technical measurement: make sure the pixel captures purchase events completely, use UTMs to cross-check website analytics, and accept 5–15% variance between measurement systems — weekly trends matter more than any single day's absolute number.