MER Calculator (Marketing Efficiency Ratio)
Calculate your marketing efficiency ratio from total revenue and total spend, then see the MER you actually need to break even at your margin — not just the MER you have.
Enter your numbers
Totals for the period
Include every marketing cost you want measured — ad spend plus agency retainers and tools if you track them that way.
Optional — unlock break-even MER and aMER
Contribution margin turns MER into a pass/fail against your break-even. New-customer revenue gives you aMER (acquisition MER), which strips out repeat orders.
Your result
MER (Marketing Efficiency Ratio)
4.00x
Total revenue ÷ total marketing spend
Break-even MER you need
2.22x
Buffer vs. break-even
+1.78x
aMER (new-customer)
2.60x
Contribution margin
45.0%
Your MER of 4.00x is comfortably above the 2.22x you need to break even. There's room to reinvest or scale spend before efficiency becomes a problem.
aMER of 2.60x is your marketing efficiency on new customers alone. It is always lower than blended MER, and it is the harder test: it shows whether acquisition pays for itself before any repeat orders.
Quick check
If your contribution margin drops 5pp (from 45% to 40%), the MER you need to break even rises to 2.50x.
Want your MER tracked against break-even automatically?
Daymark connects Shopify and every ad platform to keep MER, aMER, and margin current — grounded in your real revenue, not platform attribution.
See how Daymark tracks this live →What Is MER (Marketing Efficiency Ratio)?
Marketing efficiency ratio (MER) is your total revenue divided by your total marketing spend across every channel.
MER = Total Revenue / Total Marketing Spend
If a brand does $120,000 in revenue in a month and spends $30,000 on marketing, its MER is 4.0x. Every marketing dollar is associated with $4 of revenue. MER is deliberately blunt: it doesn't care which ad platform gets credit, because it only uses two numbers you can pull straight from your bank and your store.
That's the point. Platform ROAS can be inflated by overlapping attribution. MER can't. There is one revenue number and one spend number, so nobody double-counts. For the full definition, formula variants, and benchmarks, see the marketing efficiency ratio glossary page and what is a good MER.
How This MER Calculator Works
Enter total revenue and total marketing spend and you get your MER instantly. But the number that actually decides whether that MER is good is the one no other MER calculator shows you: the MER you need to break even.
If you add your contribution margin, this calculator computes your break-even MER:
Break-even MER = 1 / Contribution Margin %
A brand with a 45% contribution margin needs an MER of about 2.2x just to cover the marketing spend against the margin those sales produce. A brand with a 25% margin needs 4.0x. Same revenue, completely different verdict — which is why an MER of "4.2x" means nothing until you know the MER you need.
Add new-customer revenue and you also get aMER (acquisition MER): new-customer revenue divided by total spend. aMER is the harder test — it strips out repeat orders and shows whether your marketing pays for itself on acquisition alone.
MER vs ROAS
| MER | ROAS | |
|---|---|---|
| Revenue source | Your store's total revenue | Each platform's self-attributed revenue |
| Spend source | All marketing spend combined | Spend on one platform |
| Can be double-counted? | No | Yes — platforms overlap |
| Best for | Judging total marketing efficiency | Optimizing within a single channel |
| Reflects agency + tools? | Yes, if you include them | No |
ROAS answers "is this campaign pulling its weight inside its own platform." MER answers "is our marketing, as a whole, efficient enough to be profitable." You need both, but only MER is safe from attribution inflation.
Worked Example
A skincare brand doing $120,000/month spends $30,000 across Meta, Google, and a retainer agency.
| Input | Value |
|---|---|
| Total revenue | $120,000 |
| Total marketing spend | $30,000 |
| MER | 4.0x |
| Contribution margin | 30% |
| Break-even MER | 3.33x |
| New-customer revenue | $78,000 |
| aMER | 2.6x |
At a 30% margin, break-even MER is 3.33x. The brand's 4.0x clears it, but not by much — a 5pp margin slip (to 25%) pushes break-even to 4.0x, wiping out the cushion entirely. And aMER of 2.6x is below break-even MER, which means new-customer revenue alone isn't covering spend yet; profitability depends on repeat orders. A raw "4.0x MER" looked healthy; the margin-adjusted view is a warning.
When MER Misleads
- Repeat-heavy months look artificially efficient. A big month of returning-customer orders lifts MER without any new acquisition. That's why aMER matters.
- Seasonality and organic spikes. A viral moment or holiday drives revenue that MER credits to marketing spend it had nothing to do with.
- Lagged spend. Spend today builds revenue over weeks. A month where you cut spend can show a great MER purely because you're harvesting past investment.
- It won't tell you where to cut. MER is a whole-business number. It flags a problem but not which channel caused it — you still need channel-level data to act.
Use MER as the profitability floor and the headline efficiency number. Use break-even MER to judge it, aMER to test acquisition, and channel data to decide what to change.
Frequently asked questions
What is MER (marketing efficiency ratio)?
MER is total revenue divided by total marketing spend across all channels. If you do $120,000 in revenue and spend $30,000 on marketing, your MER is 4.0x. Because it uses one revenue number and one spend number, it can't be inflated by overlapping platform attribution the way individual channel ROAS can.
How do you calculate MER?
MER = Total Revenue ÷ Total Marketing Spend. Add up all marketing spend for a period — Meta, Google, TikTok, plus agency fees and tools if you track them that way — and divide your store's total revenue for that same period by it. The result is expressed as a multiple, like 4.2x.
What is a good MER?
There is no universal good MER. The right floor is your break-even MER, which is 1 divided by your contribution margin. A brand with a 45% margin needs about 2.2x to break even; a brand with a 25% margin needs 4.0x. An MER of 4.2x is strong for one and marginal for the other, so always judge MER against your own margin, not a benchmark.
What is break-even MER?
Break-even MER is the MER you need just to cover marketing spend against the contribution margin your sales produce. It equals 1 ÷ contribution margin %. If your margin is 40%, your break-even MER is 2.5x — below that, marketing spend is eating into profit even if the raw MER looks fine.
What is the difference between MER and ROAS?
ROAS uses each ad platform's self-attributed revenue against that platform's spend, so multiple platforms can claim the same sale and inflate the number. MER uses your store's total revenue against total marketing spend, so nothing is double-counted. ROAS is for optimizing inside a channel; MER is for judging whether marketing as a whole is efficient.
What is aMER (acquisition MER)?
aMER is new-customer revenue divided by total marketing spend. It strips out repeat orders and shows whether your marketing pays for itself on acquisition alone. aMER is always lower than blended MER, and it's the harder test — if aMER is below your break-even MER, you're relying on repeat purchases to be profitable.
Is MER better than ROAS for ecommerce?
For judging overall profitability, yes — MER can't be inflated by attribution overlap, so it's a more honest measure of whether total marketing spend is efficient. But MER won't tell you which channel to cut. Use MER as the profitability floor and channel-level ROAS or CAC to decide where to move budget.
What time period should I calculate MER over?
Most brands track MER monthly, and many watch a rolling 7- or 30-day MER for trend. Shorter windows are noisier because spend today builds revenue over the following weeks. Whatever window you pick, use the same period for both revenue and spend so the ratio is apples to apples.
More Free Tools for You
Blended ROAS Calculator
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Break-Even ROAS Calculator
Calculate the ROAS your store needs before any channel is profitable.
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Blended CAC Calculator
Calculate true blended CAC across all channels and check first-order profitability.
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Track MER against break-even with live store and ad data
Daymark connects Shopify and every ad platform so MER, aMER, and margin stay grounded in what your store actually recorded — not each platform's attribution.