What is MER, and what is a good one?

Updated 16 October 2026 · 5 min read

MER is the first number we look at on a Shopify store's dashboard. It is simple, hard to fool, and it answers the question every founder actually has: for every pound we put into ads, how much comes back in sales?

The short answer: MER (marketing efficiency ratio) is your total sales divided by your total ad spend. A good MER is one comfortably above your break even MER, which is 1 divided by the share of each sale you keep after product, delivery and payment costs. For many stores that lands somewhere around 2 to 3 to break even, but yours depends on your margins.

What MER is

MER stands for marketing efficiency ratio. Some people call it blended ROAS, because it blends every channel into one number.

MER = total sales ÷ total ad spend

Total sales means everything your store took, from every channel: ads, email, search, word of mouth and people who typed your address in. Total ad spend means every platform added together: Meta, Google, TikTok and anything else you pay for.

That is the difference from ROAS. ROAS takes the sales one platform claims and divides by that platform's spend. MER doesn't care which ad gets the credit. It just asks whether the whole machine is paying for itself.

A worked example

In one month a store spends:

£4,000 on Meta
£1,500 on Google Ads
£500 on TikTok

That is £6,000 of ad spend. Over the same month Shopify shows £21,000 of net sales (after discounts and refunds, before VAT and delivery).

MER = £21,000 ÷ £6,000 = 3.5

So every £1 of ad spend went with £3.50 of sales.

Why MER matters more than platform ROAS

Every ad platform measures its own results, and every one of them gives itself the benefit of the doubt. Meta, Google and TikTok can all claim the same order, and add those claims together and they often come to more than you actually sold. MER can't be double counted, because the sales figure comes from Shopify and the spend figure is what you actually paid the platforms.

It also catches what ROAS misses: the customer who saw a TikTok, searched your name a week later and bought. No platform may get the credit, but the sale still counts in MER. We go into this properly in MER against platform ROAS.

Work out your break even MER

There is no universal good MER, because it depends on how much of each sale you keep. Start with your break even MER, the point where ads pay for themselves and nothing more.

Take a typical £100 of net sales.
Take off what it costs you to fulfil: the products themselves, packaging, delivery you pay for, payment fees and any per order app costs. Say that comes to £55.
What is left is your contribution before ads: £45, or 45% of sales.
Break even MER = 1 ÷ 0.45 = 2.2.

Below 2.2, this store loses money on its ads. At 2.2 it breaks even on them, but still has rent, salaries and software to pay. So the real target sits above break even, by however much profit you need to cover those and grow.

Use net sales excluding VAT, or your MER will look about 20% better than it is. Our post on ROAS and VAT walks through why.

So what is a good MER?

Rules of thumb online usually say 3 or more. That can be right for a brand keeping around half of each sale. For a brand with thin margins, a MER of 3 can still lose money, and a brand with big margins can grow profitably well below it. Some honest guidance instead:

Below break even: your ads cost more than they bring in. Fine for a short launch push you've planned for, worrying if it lasts.
Around break even to a little above: where many brands sit when they are pushing hard for new customers, betting on repeat orders later. Only sensible if customers really do come back.
Well above break even: profitable, and often a sign you could spend more. A very high MER can mean you are underspending and leaving growth on the table.

The trend matters as much as the level. A MER that slides month after month while spend is flat tells you something is wearing out, usually the creative.

What moves MER, besides your ads

Because MER uses all your sales, things that have nothing to do with ads move it too. Keep these in mind before you praise or blame a campaign:

Returning customers and email. A strong email programme lifts sales without any ad spend, so MER rises. That is real money, but it isn't the ads.
Seasons and sales. Black Friday, Christmas and payday weeks lift sales whatever the ads do.
Spend you've left out. If you pay for Pinterest or influencers and don't count it, your MER flatters you.
Scale. MER usually falls as spend rises, because the cheapest customers are reached first. A lower MER on a bigger budget can still mean more profit in total.

Some brands also track new customer MER: sales from first time customers divided by ad spend. It is stricter and better at showing whether ads are finding new people, but it needs customer level data to work out.

MER in That Other Dashboard

That Other Dashboard works MER out the same way every day: your Shopify net sales (after discounts and refunds, before tax and delivery) divided by the spend of every ad platform you've connected. It shows it next to spend, cost per order and each platform's own ROAS, for today, month to date, the last 7 days or the last 28, always against the period before.

Because it only counts the platforms you connect, connect every one you spend on, or the MER on the screen will be kinder than the real one.

Common questions

Is MER the same as blended ROAS?

Yes. Both mean total sales divided by total ad spend across every channel. MER is the more common name among Shopify brands.

Should MER use gross sales or net sales?

Net sales, after discounts and refunds and without VAT. Gross sales count money you never keep, which makes MER look better than it is.

How often should I check MER?

Look at it daily for anything unusual, but judge it over at least a week, ideally 28 days. Single days swing with the weekday, emails and paydays.