MER.

MER, properly understood

MER = Total revenue ÷ Total ad spend. It sums every dollar of spend across every channel into the denominator and total company or store-wide revenue into the numerator, deliberately ignoring channel-level attribution entirely — that's both its strength (immune to over-attribution) and its limitation (it can't tell you which channel to cut or scale). Revenue comes from finance or the e-commerce platform (Shopify, POS, ERP), while spend comes from aggregated ad billing across channels — reconciling the two on the same time window, matching order date to spend date rather than payment-clearing date, is where most MER calculation errors creep in.

MER during Ramadan and Eid needs careful reading — spend typically ramps faster than revenue in the first days of a seasonal push, as shoppers browse before buying closer to Eid, so a weekly MER read during the ramp-up can look worse than the campaign's true efficiency; look at MER across the full campaign window rather than week by week during these peaks. In markets with heavy cash-on-delivery, "revenue" recorded at order time doesn't equal revenue actually collected — a spike in COD non-collection or post-Ramadan returns can retroactively worsen a MER a marketer already reported as healthy.

MER is a blunt instrument — it can't diagnose which channel is underperforming, and a healthy overall MER can hide one channel wasting spend while another quietly overperforms. It's also sensitive to non-marketing revenue drivers — a price change, a viral organic moment, a competitor stockout — that have nothing to do with ad spend, so a rising MER doesn't automatically validate the marketing plan. Don't use MER alone to make channel-level budget decisions; it can only tell you whether the whole system is working, not which parts.

Pair MER with channel-level ROAS to allocate budget within the mix, and with incrementality testing or MMM to understand true channel contribution underneath the blended number.

MER also tends to trend upward on its own as a brand's organic and branded-search demand grows, independent of paid efficiency improving, because a larger share of total revenue increasingly comes from people who would have bought anyway — this is a real dynamic worth naming rather than a flaw in the metric, but it means a rising MER over a brand's lifecycle should be partly credited to brand-building and word-of-mouth, not read purely as evidence that this month's paid campaigns got more efficient. It's also worth calculating MER on both a blended, all-channel basis and a paid-only basis that excludes influencer or affiliate spend that's harder to size consistently, since folding an inconsistently-tracked spend category into the denominator can make the ratio swing for reasons that have nothing to do with paid media performance — a clean, consistently-scoped MER series over time matters more than getting any single period's number perfectly precise.