# Marketing Efficiency Ratio: The One Number That Survives Attribution Arguments

Source: https://attributionplaybook.com/blog/2026-11-12-marketing-efficiency-ratio-attribution-arguments.html

November 12, 2026

*Marketing Efficiency Ratio is total revenue divided by total marketing spend, usually blended across all channels. It cannot be inflated by an attribution window, because it does not use one. When the platforms disagree, MER is the number that tells you whether the business actually grew.*

## The argument that never ends

Meta reports 150 conversions, GA4 says 110, HubSpot says 90, and the store sold 100 orders. Everyone in the meeting is right about their own number and wrong about the business, because each platform credits itself inside its own window. Meta counts 7 days after a click and 1 day after a view. Google Ads defaults to a 30-day click window. GA4 uses a 90-day lookback for key events. One order can be credited by all three at once, and the sum of the platform reports is always larger than the store's actual sales. The argument about which platform deserves the credit can run for years, and it has, in most marketing teams.

Marketing Efficiency Ratio ends it by refusing to play. MER is total revenue divided by total marketing spend, blended across every channel, with no attribution model, no window, and no last-click rule. It answers the only question the business actually has: for every dollar we spent on marketing, how many dollars of revenue came back? A MER of 2.1 on a 7-day window and a MER of 2.8 on a 90-day window are not two different businesses. They are the same business measured with two different rulers, and the ruler is the thing that changed, not the business.

## How to use it without fooling yourself

MER has two honest limits, and both should be stated out loud. First, it is blended, so it cannot tell you which channel to cut. A channel with a terrible ROAS can hide inside a healthy MER, and a channel with a great ROAS can be starved because the blended number looked fine. Use MER for the budget decision and channel ROAS for the allocation decision, and never let one do the other's job. Second, MER moves with things that are not marketing: a price change, a stockout, a seasonal swing, a product launch. A MER that fell after a price increase is not a marketing failure, and a MER that rose during a stockout is not a marketing win.

The working cadence is weekly: total revenue from the store, total spend from every platform, one ratio, tracked over time. When a platform's reported ROAS jumps and MER does not move, the platform's window moved, not the business. When MER moves and no platform's ROAS explains it, something outside marketing changed, and that is worth knowing too. Attribution settings affect reporting and optimization, not the actual number of sales. MER is the check that keeps the reporting honest. The incrementality check behind this is [geo holdouts on a small budget](https://attributionplaybook.com/blog/2026-11-10-meta-7-day-click-1-day-view-vs-ga4.md), and [promo codes stealing credit from organic search](https://attributionplaybook.com/blog/2026-11-10-promo-code-attribution-organic-cannibalization.md) is the same misattribution wearing a different label.

## Frequently asked questions

### What is Marketing Efficiency Ratio?

Total revenue divided by total marketing spend, blended across all channels. It has no attribution window and no model, so it cannot be inflated the way a platform ROAS can.

### Does MER replace channel ROAS?

No. MER answers whether the business grew; channel ROAS answers where to spend next. A bad channel can hide inside a healthy MER, so use both, for different decisions.

### Why do platform ROAS numbers never match MER?

Because each platform credits itself inside its own window, and one order can be credited by several platforms at once. MER uses the store's own revenue total, which cannot be double counted.

### How often should I track MER?

Weekly, as a trend. A single week is noise; a rising or falling trend over a month is signal, and it should be read alongside price, stock, and seasonality, not alone.