MER: The Marketing Metric You Didn't Know You Needed

All marketers are obsessed with attribution these days, and with good reason. Why wouldn’t you want to know exactly how much you’re making from each £ you’re spending?

But, there is a more holistic theory that complements all the granular attribution work you’re doing, and it doesn’t nearly get enough airtime. 

Meet MER, or Marketing Efficiency Ratio, or sometimes called Media Efficiency Ratio too.

So what is it? 

MER is refreshingly simple. Take your total revenue, divide it by your total media spend across every channel and platform that you’re running paid activity on, and you’ve got your number. It could be 2, 3, 10. That’s your MER - one clean figure that tells you how much your marketing investment is performing as a whole, rather than channel by channel. 

Some marketers fold in other costs too, such as team salaries, production costs, etc. And others prefer to flip the formula and show it as a percentage. It's worth bearing in mind, though, that if you leave out costs that fluctuate a lot, you might find it loses some of its reliability over time.

But here’s the thing: there’s no wrong answer. MER is an internal compass, not an external report. You get to define it in whatever way is the most useful for your business.

Bigger isn’t always better

You’d be forgiven for thinking that “the higher the MER, the better”. But just like ROAS, it works best as a target rather than a trophy. The real question MER helps you answer isn’t just "how is my marketing performing?" It’s "how much more can I confidently spend?" That’s where it gets exciting. 

There are data marketeers and there are gut marketeers - nothing wrong with being either, as long as each is willing to occasionally borrow a page from the other’s playbook. If you lean more towards gut instinct, you’ve got ideas. Strong ones. But they’re tricky to attribute without precision. MER can be your new best friend. It gives you a framework to test those instincts responsibly and shows you exactly how much room you have to play with. 

Here’s a quick example to bring it to life: 

You calculate you can run profitably and hit your targets for 2026, provided your MER is above 3.

• In Q1, you spend £100k and exceed your targets, bringing in £420k revenue.
• In Q2, you forecast £100k spend for £300k revenue.
• If you were to hit your current Q2 forecast, that would  be an H1 total of £720k revenue from a £200k spend. 
• If you are bringing in £720k then you can afford to spend up to 720k/3 = £240k on advertising, without missing your MER target, even though your initial budget was £200k.
• Therefore, due to your strong Q1, you have £40k additional to play with for Q2, so you could confidently test new opportunities. You would still be in the position where hitting your target revenue would mean hitting your target MER.

The bottom line

When you’re running a complex, cross-channel marketing strategy, it’s easy to get lost in the weeds of platform-level metrics. MER pulls you back up to view from the top - a single, honest number that tells you whether the whole machine is working. Simple to calculate, genuinely useful, and one of those metrics that, once you start tracking it, you’ll wonder how you ever managed without. 

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