MER Calculator: Blended Return on All Ad Spend

Calculate your MER

What MER measures

MER answers one question: for every dollar of paid media, how many dollars of business revenue came in? The numerator is the whole business — paid, organic, and direct revenue together. The denominator is every paid channel combined. Nothing is attributed; nothing is assigned to a platform.

Channel ROAS answers a narrower question: for every dollar spent in this channel, how much revenue did this channel claim? Both metrics are ratios, but their revenue scopes differ, so they are not interchangeable.

Why MER usually trails channel ROAS

Ad platforms report on overlapping credit. A customer who sees a Meta ad, later searches on Google, and then buys can be claimed by both platforms. Add the platforms' attributed revenues together and you can exceed the store's actual revenue — the same order counted twice. MER cannot be inflated this way because its numerator is a single audited total: what the business actually earned.

This creates the classic trap: each channel dashboard shows a healthy ROAS, spend keeps rising, yet the business-level return barely moves. When you optimize channel ROAS in isolation, you can end up buying the same conversions twice while MER quietly falls.

Worked example

Illustrative inputs: a store earns $22,000 in total revenue and spends $8,000 on paid media. MER is $22,000 ÷ $8,000 = 2.75×, or 275%. The split view tells the fuller story: Google claims $16,000 from $4,000 of spend (4.0×) and Meta claims $14,000 from $4,000 (3.5×) — $30,000 of attributed revenue against $22,000 of actual revenue. The $8,000 gap is overlapping attribution, and it is exactly why the blended 2.75× is the number to plan against.

When to use each metric

Use MER for business-level decisions: setting the total ad budget, judging whether paid media as a whole is pulling its weight, and reporting to anyone who cares about the P&L rather than a dashboard. Use channel ROAS for in-channel decisions: comparing two campaigns inside the same platform, where the attribution rules are at least consistent. Never add channel ROAS values together and never treat their average as a business result.

Limits

MER is a guardrail, not a proof. It does not show incrementality — revenue that would have arrived without any ads still counts in the numerator, so a high MER does not prove the ads caused the sales. It cannot separate brand from non-brand spend, new from returning customers, or one channel's true contribution from another's. It also moves with things advertising does not control: pricing, promotions, seasonality, and stock levels all change total revenue. Define the revenue scope once (net of refunds is the honest choice) and keep it fixed before comparing MER across periods.

Examples are illustrative, not client results or benchmarks. The calculations use the inputs shown; real-world decisions depend on your records and assumptions. Report a correction.