MER CALCULATOR
MER & nCAC Calculator
The blended, attribution-proof numbers that tie your ad spend to the P&L. Marketing efficiency ratio, new-customer CAC, and acquisition MER.
Why blended beats platform ROAS: read the number that doesn't lie in the measurement guide.
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How to use this calculator
Enter your total ad spend and total revenue for a period to get your MER, the blended return that ties directly to your profit and loss. Add your new-customer count, new-customer revenue and gross margin to also see your new-customer CAC, your acquisition MER, and your break-even MER. Everything updates as you type, and the optional fields fill in the extra cards.
What MER, nCAC and aMER mean
MER (marketing efficiency ratio), also called blended ROAS, is total revenue divided by total ad spend across every channel. Because it does not care which platform claims a sale, no amount of attribution double-counting can inflate it. It is the honest topline.
New-customer CAC (nCAC) is spend divided by new customers, which strips out the returning buyers a platform will happily claim as fresh wins.
Acquisition MER (aMER) is revenue from new customers only, over total spend. Blended MER can be flattered by repeat purchases, so aMER isolates how well your spend brings in genuinely new revenue. The gap between MER and aMER is roughly what repeat buyers are carrying.
What is a good MER?
There is no universal good MER, because your floor is set by your margin. Your break-even MER is the inverse of your gross margin: at 50% you need 2.0x to break even, at 25% you need 4.0x. A good MER is comfortably above your own break-even, and the right way to use it is as a trend watched against the P&L, not as a number compared to an industry benchmark. If your MER is healthy while platform ROAS looks weak, you are probably profitable and mis-measuring.
A worked example
Spend €50,000, make €200,000, and your MER is 4.0x. At a 50% margin your break-even MER is 2.0x, so blended spend is comfortably profitable. If 2,000 of those sales were new customers, your nCAC is €25. If new customers drove €120,000 of the revenue, your aMER is 2.4x, and the gap between the 4.0x blended MER and the 2.4x aMER shows how much of the topline your repeat buyers are carrying.
MER versus platform ROAS
Platform ROAS is revenue a platform attributes to its own ads over that platform's spend, and since iOS 14 those numbers over-credit themselves and overlap across channels. MER cannot be gamed that way, because it is everything over everything. Use platform ROAS to steer individual campaigns day to day, and use MER to judge whether the whole engine is profitable. For the full picture, see the measurement guide.
Common questions
MER is total revenue divided by total ad spend across all channels in a period. Because it ignores which channel claims each sale, it cannot be gamed by attribution, which makes it the honest, board-level view of whether your marketing is working. It is sometimes called blended ROAS.
New-customer CAC is total ad spend divided by the number of new customers acquired in a period. It strips out returning buyers that platforms love to claim as fresh wins, so it is a cleaner read on what you actually pay to acquire someone new.
There is no universal figure, because your break-even MER is the inverse of your gross margin. At a 50% margin you need 2.0x to break even, at 25% you need 4.0x. A good MER is comfortably above your own break-even, watched as a trend against the P&L, not compared to an industry average.
ROAS is revenue a platform attributes to its own ads over that platform's spend, and different platforms double-count the same sale. MER is total revenue over total spend across everything, so it cannot be inflated by attribution. Use platform ROAS to steer campaigns and MER to judge the whole engine.
Acquisition MER is revenue from new customers only, divided by total ad spend. Blended MER includes returning-customer revenue, which can flatter your numbers, so aMER isolates how efficiently your spend brings in genuinely new revenue. The gap between MER and aMER is roughly the share carried by repeat buyers.
Since iOS 14, platform-reported ROAS over-credits itself and channels claim the same conversions, so the numbers do not add up to reality. MER ties directly to the P&L and cannot be gamed. If MER is healthy while platform ROAS looks poor, you are probably profitable and mis-measuring.
Related: the paid social measurement guide, the incrementality calculator, and the break-even calculator.