MER
Whether the whole business is buying its sales at a price you can live with.
What it means
MER is your Ad Spend divided by your Total Sales, written as a percentage: the share of everything you sold that went back out on advertising. It measures every connected ad channel against all store sales, not one platform against the sales that platform claims, so no attribution decision touches it.
Lower is better here, and that is the opposite of the usual convention. Elsewhere MER normally means sales divided by spend, where 3.0 is healthy and bigger is better. In this app it's spend divided by sales, graded excellent at 30% and poor at 45%. Read a 42 as a strong month and you have read it upside down. ROASROASRevenue earned for every ad dollar spent.4 or more is healthy is the right-way-up version of the same two numbers.
Show the math
Formula and a worked example
Ad SpendAd SpendRead it next to ROAS and sales; spend only helps if the return holds. is every connected ad channel added together for the period — with Amazon included on Summary when Include Amazon is switched on.
Total SalesTotal SalesYour true top line and the anchor for every efficiency metric. is all store sales over the same period, not the portion any platform credits to itself.
It reads as a percentage and lower is better. 30% means thirty cents in every euro you took paid for the advertising.
Worked example. March: €18,000 of Ad Spend against €60,000 of Total Sales. MER = 18,000 ÷ 60,000 = 30%. The ROAS card on the same page reads 60,000 ÷ 18,000 = 3.3. One fact, written two ways — if you have read both cards, you have read one number.
Nothing in this is attributed, and that cuts both ways. No platform can inflate it by crediting itself, and it will never tell you which platform earned what.
It answers the question
How much of everything you sold went on advertising? At 30% the answer is thirty cents in the euro, and the next question is whether the other seventy cover product, fees, shipping and the rest of the business with something left over.
Why it matters
It's the one advertising number no platform can flatter. Every attributed metric depends on a platform deciding which sales were its doing, and every platform decides generously. MER divides one bill by one revenue figure, and you can check both against your bank.
That also makes it the number to build a budget from. Decide the MER you're willing to run at and next period's spend follows from your sales forecast rather than from last period's habit. The published band is a starting point, not the limit — the real ceiling is your own margin, because whatever MER you run has to fit inside what's left after product cost, fees and shipping.
What good looks like
Lower is better, so the healthy end of this scale is the left one. Expect this card and the ROASROASRevenue earned for every ad dollar spent.4 or more is healthy card beside it to disagree at the edges: 30% here is a ROAS of 3.3, while ROAS is graded excellent at 4 — which would be 25% here. Two bands, one number, and neither is the threshold that decides anything. That one is your margin.
How to improve it
| Lever | What you do | Expect | How long | Watch out for |
|---|---|---|---|---|
| Fast Cut the spend that never became a sale | Sort campaigns by spend, look across at the sales column, and pause the rows with spend and no orders over two full weeks | MER down, spend down | 1–2 weeks | You improved the ratio by shrinking. Total Sales usually falls with it, so read the sales line beside the ratio or a retreat reads as a win. |
| Fast Move budget to the channel carrying the period | Compare each channel's spend against the sales in the same period, then reset the daily budgets | The same total spend against a lower MER | 1–2 weeks | Concentrating budget makes the whole business depend on one platform's pricing. The month it turns expensive, there's nowhere left to move to. |
| Slow Sell more to the customers you already have | Work the email and SMS lists and the repeat purchase, so sales arrive without a media bill behind them | Total Sales rises while Ad Spend holds flat | 1 quarter | Sending harder to hit the number costs list health, and an unsubscribe is permanent in a way a bad ad week never is. |
| Slow Fix what the paid traffic lands on | Improve the product pages and checkout your ads point at, so the same spend turns into more revenue | MER falls with no budget change at all | 1 quarter | Site work never shows up in an ad account, so the gain gets credited to whatever budget change happened the same week — and the wrong lever gets pulled again next quarter. |
Every lever costs something somewhere. The last column is the one to read twice.
Read it with
A ratio improves when the top falls or when the bottom rises, and those are opposite situations. Read it against sales or you can't tell growth from retreat.
Scaling efficiently
More revenue for a smaller share of it spent. The rare corner, and the one worth pushing into before whatever caused it goes away.
Bought the growth
Revenue is up and a bigger slice of it paid for the ads. A decision rather than a fault, as long as the slice still fits inside your margin.
Cheaper and quieter
A better ratio on less revenue usually means less advertising, not better advertising. This is the corner where stores under-invest and congratulate themselves.
The real alarm
Less revenue and a larger share of it going to ads. The cause sits outside the ad accounts as often as inside them, so check the site before the bids.
The ratio moves for two different reasons and only the spend line says which. MER climbing while Ad Spend sits flat means the money is doing less than it was, and no budget decision caused it. MER climbing alongside spend means you chose this — the only question left is whether you'd choose it again.
On Marketing these two divide the same pair of numbers in opposite directions, so they can never disagree about direction — only about where the line sits. 30% here is a ROAS of 3.3, and ROAS grades excellent at 4. When one card says excellent and the other doesn't, you're looking at two bands, not two findings.
Common misreads
Not in this app. Here MER is Ad Spend ÷ Total Sales as a percentage and lower is better, so 42% is nearly at the poor band of 45%. The convention you're thinking of divides sales by spend, and ROAS is the card that does that.
The denominator is all your sales, including the repeat orders and organic traffic no ad ever touched. A store with a strong list and loyal customers can post a healthy MER while its advertising earns very little. This is a measure of the business, not of a campaign.
It's one blended figure across every connected channel. A channel wasting money sits invisibly inside a healthy total until it grows big enough to move it. Read the per-channel spend columns before deciding nothing is wrong.
Also called
Marketing Efficiency Ratio · media efficiency ratio · blended marketing efficiency · ad spend as a share of sales
See yoursYour MER for the period, next to the Ad Spend and the Total Sales it divides.
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