The strong results an ecommerce brand sees in its ad dashboards don't always show up in total sales to the same degree. ROAS in Google Ads campaigns can rise while the business's revenue grows more slowly, or the conversion revenue reported by Meta Ads can differ from actual sales. In these cases, MER (Marketing Efficiency Ratio) divides total sales revenue by ad spend to show the overall efficiency of the budget. Alongside campaign performance, you also need to track the relationship between the business's total sales and its ad spend.
What Is MER and How Is It Calculated?
The calculation rests on two data points: the business's total sales revenue and its spend on paid media channels. Spend across Google Ads, Meta Ads and other ad platforms is added together. On the revenue side, you use the business's actual sales rather than the conversion values reported by the ad dashboards.
The MER formula:
MER = Total Revenue / Total Marketing Spend
In this article, MER is calculated as total sales revenue divided by paid media spend. If your calculation also includes agency fees, creative production and other marketing costs, the result will differ.
Say an ecommerce brand has a monthly ad spend of TRY 500,000 and total sales revenue of TRY 2,500,000.
Metric | Monthly Value |
Google Ads spend | TRY 300,000 |
Meta Ads spend | TRY 200,000 |
Total ad spend | TRY 500,000 |
Total sales revenue | TRY 2,500,000 |
MER | 5 |
For every TRY 1 of ad spend, TRY 5 of total sales revenue was generated in the same period. Orders from organic search, direct traffic and other sources may also be included in total revenue. This calculation does not show how much of your sales came directly from ads.
Which Data Is Included in the MER Calculation?
When calculating ad costs, you add up spend on any other paid media channels you use in addition to Google Ads and Meta Ads. On the sales side, revenue from your website and any other channels within scope is used. Whether marketplace revenue is counted depends on the business's reporting scope.
Some brands also add agency fees, creative production costs and other marketing costs to the calculation. You may also come across different presentations in reporting systems. For example, an MER of 5 corresponds to an ad spend-to-revenue ratio of 20%, calculated from the same data.
To get comparable results, you should decide in advance how VAT, returns, cancellations and marketplace revenue are handled. In product categories with long purchase cycles, there can be a gap between the date of ad spend and the date of the sale. In such cases, weekly or monthly comparisons can be more meaningful than daily fluctuations.
What Is the Difference Between ROAS and MER?
Ad teams usually rely on ROAS when reviewing campaign performance. ROAS (Return on Ad Spend) is the ratio of the conversion value attributed to a specific campaign or channel to its ad cost. MER, which compares all of the business's sales with ad spend, is based on a broader scope of revenue.
Criterion | ROAS | MER |
Calculation | Attributed revenue / Ad spend | Total revenue / Total ad spend |
Measurement scope | Campaign, ad group or channel | Total sales and ad budget |
Attribution impact | Depends on the platform's attribution model | More independent of platform attribution models |
Purpose | Campaign and channel optimization | Overall advertising efficiency |
Core decision | Which campaign should get budget? | How efficiently is the total budget working? |
In a month when Google Ads reports a ROAS of 5 and Meta Ads reports a ROAS of 4, it is not correct to add the two values together to calculate the business's total advertising return. The same order can be reported in more than one ad account because platforms use different conversion windows and attribution models.
The performance campaigns appear to deliver also depends on the conversions defined in the ad account. Which conversion actions are measured in Google Ads and how those actions are assigned value both affect the reported ROAS. For more detail on calculating and interpreting it, see our article What Is ROAS and How Is It Calculated?
What Is the Difference Between MER, ROAS and ROI?
Seeing how ad spend relates to sales may not be enough to understand how much the investment earned. ROI (Return on Investment) measures the net return an investment generates after costs. While ROAS and MER are revenue-based ratios, ROI compares the net gain with the cost of the investment.
Metric | Core Question | Calculation |
ROAS | How much sales return does the ad report? | Attributed revenue / Ad cost |
MER | How much was sold relative to the total ad budget? | Total revenue / Total ad spend |
ROI | How much did the investment earn after costs? | Net investment gain / Investment cost × 100 |
Suppose TRY 400,000 in sales is attributed to a campaign and TRY 100,000 was spent on ads. If the variable costs of those sales, excluding advertising, are TRY 240,000, a contribution of TRY 60,000 remains after ad spend. That amount is 60% of the ad spend. Because the calculation assumes all attributed sales came from the ads, it should not be treated as true incremental ad ROI.
This ratio is a simplified ad ROI example that assumes all sales happened because of the ads. Since fixed operating expenses and other investment costs are not included, it should not be interpreted as the business's net profit or as a proven incremental return on advertising.
Why Does MER Fall While ROAS Rises?
When a brand's ad spend grows faster than its sales revenue, the total revenue-to-spend ratio can decline even if the ROAS reported by campaigns goes up.
Metric | Previous Month | Last Month |
Ad spend | TRY 400,000 | TRY 600,000 |
Total revenue | TRY 2,400,000 | TRY 3,000,000 |
MER | 6 | 5 |
Google Ads ROAS | 4.2 | 4.8 |
Meta Ads ROAS | 3.6 | 4.1 |
Sales revenue grew 25% while ad spend grew 50%. Even though Google Ads and Meta Ads reported higher ROAS, total MER fell from 6 to 5.
Although the business's revenue increased, advertising costs rose faster. The financial outcome of this gap depends on whether the contribution left from the additional sales covers the higher ad costs.
Can MER Rise While ROAS Falls?
In periods when organic sales or revenue from existing customers grow, the ROAS values of ad platforms can fall while the business's overall efficiency ratio rises. If a brand's ad spend rises from TRY 400,000 to TRY 450,000 and its sales revenue rises from TRY 2 million to TRY 2.7 million, MER goes from 5 to 6.
In the same period, the conversion revenue reported by the platforms may grow or shrink at a different pace. You should separately investigate how much of the sales increase was driven by brand searches, repeat purchases, seasonal demand or paid campaigns.
Can Total Revenue Fall While MER Rises?
MER can rise even when total revenue declines after budget cuts. Suppose a brand that cut its monthly ad spend from TRY 500,000 to TRY 200,000 saw its sales revenue fall from TRY 2 million to TRY 1.5 million.
Metric | Previous Period | Latest Period |
Ad spend | TRY 500,000 | TRY 200,000 |
Total revenue | TRY 2,000,000 | TRY 1,500,000 |
MER | 4 | 7.5 |
Because ad costs fell faster, MER rose from 4 to 7.5 while total revenue dropped 25%. The loss in sales volume may be an undesirable outcome given the brand's growth goals.
In a situation like this, you should examine which product groups and customer segments the budget cut affected. You should also check the change in overall profitability to understand how the higher MER translated into results for the business.
What Should a Good MER Be in Ecommerce?
Because businesses have different cost structures, there is no fixed MER that everyone should aim for. Product cost, shipping, commissions and other per-sale expenses determine the level at which the ad budget can work efficiently.
When you subtract product-level and order-level variable costs from sales revenue, you get the pre-advertising contribution margin. Using this margin, you can calculate the break-even MER needed to cover ad spend.
Break-even MER for ad spend = 1 / Pre-advertising contribution margin
Pre-Advertising Contribution Margin | Break-Even MER for Advertising |
20% | 5 |
25% | 4 |
30% | 3.33 |
40% | 2.5 |
50% | 2 |
Consider a business with a 25% pre-advertising contribution margin and total sales revenue of TRY 400,000 that spends TRY 100,000 on ads. At an MER of 4, the TRY 100,000 contribution left from sales covers the ad cost. This calculation shows the business's overall post-advertising contribution; it does not prove that the ads actually broke even.
Once rent, payroll, software and other fixed costs are added, a higher ratio may be needed to turn a profit. When setting a target, you should also factor in your growth plan and desired profit level.
How Should MER and ROI Be Interpreted Together?
Two brands with the same ad spend and sales revenue can have different profitability. For example, if two businesses each generate TRY 500,000 in total revenue on TRY 100,000 of ad spend, both have an MER of 5. Say the first brand has a pre-advertising contribution margin of 35% and the other 15%.
For the first business, the pre-advertising contribution is TRY 175,000, and TRY 75,000 remains after ad spend. For the second, the pre-advertising contribution is TRY 75,000, so after subtracting the ad cost the result turns negative at TRY 25,000.
The fact that financial results differ even though sales and spend are identical shows why MER and profitability need to be evaluated separately. To calculate true advertising ROI, you also need to know the incremental portion of sales that came from ads and the related costs.
How Do You Manage the Ad Budget Based on MER?
When the budget increases, you reach a wider audience, but customer acquisition costs can also rise. So even if your current MER is high, additional ad spend may not maintain the same sales efficiency.
In the earlier scenario, ad spend rose from TRY 400,000 to TRY 600,000, and total revenue rose from TRY 2.4 million to TRY 3 million.
Period incremental revenue-to-spend ratio = Change in revenue / Change in ad spend
600,000 / 200,000 = 3
Between the two periods, every additional TRY 1 of ad spend corresponds to a TRY 3 increase in total revenue. Because seasonality, organic sales and other revenue sources are not separated out in this calculation, the ratio does not directly prove the additional revenue created by ads. Where necessary, the true incremental effect of advertising can be investigated with incrementality tests or suitable causal analysis methods.
Does a Drop in MER Always Mean You Should Cut the Budget?
If the pre-advertising contribution margin on the additional TRY 600,000 in sales revenue is 40%, it generates a TRY 240,000 contribution. After subtracting the additional TRY 200,000 in ad costs, a positive result of TRY 40,000 remains.
If the contribution margin is 25% for the same revenue increase, the pre-advertising contribution is TRY 150,000. After the additional ad spend, the result turns negative at TRY 50,000.
Even when the ad budget and the increase in sales are the same, the business's cost structure changes the financial outcome. These calculations assume comparable periods; they do not directly show the causal return of advertising or the business's net ROI.
To make budget decisions easier, changes in ROAS and MER can be interpreted as follows:
Performance Situation | What to Examine |
ROAS rising, MER falling | Increase in total spend and the contribution margin of the additional sales |
ROAS falling, MER rising | Organic sales, repeat purchases and seasonal effects |
MER rising, total revenue falling | Impact of the budget cut on sales volume |
MER falling, contribution margin improving | Contribution the additional sales leave after ad costs |
Making the same budget decision in every scenario may not be right. CPA, new customer acquisition, stock levels and the profitability of sales should also be part of the evaluation.
Common Mistakes in MER Calculation
If a brand includes only website revenue in the first month and adds marketplace sales to the calculation in the next, MER can look different from what it really is. Because the revenue scope changed between the two periods, the resulting difference cannot be interpreted directly as a performance increase.
A high MER also does not guarantee that the business is profitable. Product cost, commissions, logistics and other expenses can reduce the contribution left from sales. When assessing financial results, you should also use indicators such as ROI and net profit separately.
During periods such as November discounts, total sales may grow while ad spend rises even faster. This can pull MER down. In addition to comparing with the previous month, looking at the same campaign period last year helps you interpret seasonal demand changes more accurately.
Another mistake is adding up the conversion values reported by Google Ads and Meta Ads to calculate the business's total sales revenue. Because the same order can be reported by more than one platform, the business's own reliable records should be the basis for sales revenue.
Tracking MER and ROAS with AdsLuma
Bringing together data from different ad dashboards can be time-consuming, especially for brands that use multiple channels. AdsLuma supports monitoring performance indicators from connected Google Ads and Meta Ads accounts in a single shared dashboard.
When you review campaign ROAS and CPA results together with changes in total MER, it is easier to see how spend increases relate to sales efficiency. You should also verify the scope of the total revenue data and ad costs you use.
Frequently Asked Questions About MER
How is MER calculated?
MER is calculated by dividing total sales revenue by total ad spend in the same period. For example, an ecommerce business with TRY 2 million in revenue and TRY 400,000 in ad spend has an MER of 5. When comparing different periods, the same revenue and cost items should be used.
What is the difference between MER and ROAS?
ROAS uses the revenue attributed to specific advertising activities, while MER compares the business's total sales with the ad budget. ROAS is used more often for campaign optimization, and MER is used more often to monitor overall budget efficiency.
Are MER and ROI the same thing?
The two metrics measure different outcomes. MER shows the ratio between sales revenue and ad spend, while ROI calculates how much return an investment generated after costs. A business with a high MER can have a low or negative ROI.
What should a good MER be?
The right MER target depends on the business's pre-advertising contribution margin and growth plan. For example, for a brand with a 25% contribution margin, the simplified break-even MER for ad spend is 4. A higher ratio may be needed to cover fixed costs and generate profit.
Can you increase the ad budget while MER is falling?
A budget increase can be sustained when the additional sales leave enough contribution after ad costs. Before deciding, compare total revenue, CPA, customer acquisition and variable costs. Because seasonal demand shifts can also affect MER, you shouldn't act solely on whether the ratio rises or falls.
