What questions do CAC, ROAS and MER answer?
Begin a performance marketing review by defining metric scope. ROAS divides revenue attributed to advertising by the relevant advertising spend. CAC divides the chosen acquisition cost by new customers acquired. In this guide, MER divides the selected total-revenue measure by total marketing expenditure for the same period.
Write down what ‘total’ includes. Are advertising, production, agency fees, tools and team costs included? Is revenue gross or adjusted for discounts and refunds? If CAC includes media cost only, label it as an ad-cost scope rather than compare it without explanation to a broader acquisition-cost measure. Likewise, a media-only ratio should not silently replace a wider MER definition in the same trend chart.
Do not equate new customers with orders. One person can place several orders in a period. Keep period, currency, cancellation and refund treatment, and identity matching in the same measurement dictionary. When the denominator is zero, state that the ratio cannot be calculated rather than generate an artificial result. These definitions are the basis for a useful comparison.
ROAS question
Under this report’s attribution conditions, how much revenue is credited per unit of advertising spend? The ratio does not independently explain net business profit.
CAC question
What is the average cost of acquiring a new customer under the chosen expense scope? The denominator is new customers and the numerator needs an explicit cost definition.
MER question
How does selected total revenue compare with total marketing expense? The ratio does not isolate the causal contribution of one campaign.
Work through an original example using one period
For an ecommerce management review, consider the following entirely illustrative scenario. These figures are neither a Prix project result nor a quotation. A store reports TRY120,000 under its chosen net-revenue definition and TRY30,000 in total marketing costs. An advertising report attributes TRY80,000 to TRY20,000 in media spend.
Advertising ROAS is 4 and MER is 4, but identical values do not mean identical measures. Suppose explicitly allocated acquisition costs are TRY24,000 and 100 customers meet the new-customer definition. That scoped CAC is TRY240. Acquisition cost differs from total marketing expense here; the remaining expenditure can serve other purposes such as retention.
Now assume TRY70,000 of non-marketing variable product and service costs are deducted from the example’s net revenue. Deducting marketing as well leaves TRY20,000. This is illustrative contribution before fixed costs, financing and tax, not net profit. With the same ROAS, higher returns or logistics costs could leave less in the business. The example demonstrates why the ratios need an accompanying cost view.
| Measure | Illustrative calculation | Meaning |
|---|---|---|
| Advertising ROAS | 80,000 / 20,000 = 4 | The advertising report’s attributed ratio |
| MER | 120,000 / 30,000 = 4 | Defined revenue / total marketing cost |
| Acquisition CAC | 24,000 / 100 = TRY240 | Defined acquisition cost / new customers |
| Illustrative contribution | 120,000 - 70,000 - 30,000 = TRY20,000 | Amount before fixed costs, financing and tax |
FROM READING TO A NEXT STEP
Clarify the definitions behind the growth report
Share revenue and cost scope, advertising reports and customer definitions. We can connect the ratios to a comparable decision record.
Reconcile advertising attribution with store records
In a measurement implementation, correct purchase events, values and currency do not make every report attribute the same sale to the same channel. Adding revenue from two platforms can count one journey twice. Review channel attribution and store-level revenue at separate levels, documenting each report’s purpose and crediting conditions.
Before changing budgets, check duplicate events, incorrect values, different periods and refund treatment. Improved measurement can increase reported revenue without proving an equivalent increase in real sales. Record the inspection date if recent figures are still updating. If definitions changed, show the break in the historical trend instead of comparing unlike periods as continuous performance.
MER can provide a business-level comparison without relying on one channel’s attribution. It still does not establish how much total revenue was caused by additional advertising. Existing customers, organic demand and seasonality affect the total. Rather than assume the same ratio will persist after increasing spend, evaluate that assumption through a controlled learning plan.
Assess growth alongside product mix and contribution
An average order value improvement should not be chosen merely to improve a marketing ratio. Larger baskets can be created through discounts, shipping subsidies or products with limited contribution. Product cost, payment fees, packing, delivery support and returns make the commercial meaning clearer.
A simplified break-even advertising ratio depends on the contribution rate before advertising; do not confuse that with product gross margin alone. Under an entirely illustrative 30% pre-advertising contribution assumption, 1 / 0.30 is approximately 3.33. That simplified threshold does not resolve fixed costs, financing, tax or future customer value, and does not replace the actual business plan.
New and returning customers can have different product mixes and behaviour. A period average may hide an unsuitable segment. Develop targets with finance and operations after verifying definitions and costs. A universal ‘good ROAS’ or ‘good CAC’ number ignores those differences. Use the ratios as part of a specific operating assessment rather than an automatic spending rule.
Connect a metric movement with a specific next test
Retention activity such as ecommerce email flows can affect total revenue. Do not treat that change as identical to new-customer advertising success. At a weekly or monthly review, establish which ratio moved, whether its definition remained stable and which customer group changed.
If ROAS rises while new-customer volume falls, investigate existing-customer or brand-demand weight. If CAC rises, first verify customer identity and expense scope, then review creative, offer and landing-page fit. If MER changes, make revenue, cost and stock conditions visible in one record. These patterns suggest hypotheses; one metric does not establish the cause with certainty.
The decision file should contain the observation, assumption, test scope, owner and review condition. Spending boundaries and stopping criteria depend on the business’s own cash and operational plan. A useful report explains what the team will validate and why it will make a decision, instead of displaying three ratios on attractive cards without a practical action.
BEFORE YOU DECIDE
Frequently asked questions
Does a ROAS of 4 mean we are profitable?
Not by itself. Review revenue definitions, attribution, product and fulfilment costs, discounts, returns and other expenses. The same ROAS can produce different contribution under a different product mix or operating cost structure.
Is CAC the same as cost per order?
No. CAC measures defined new-customer acquisition, while a cost-per-order measure may include repeat purchases. Document expense scope and the new-customer definition. Using the same label for both creates a misleading comparison.
Should agency and creative costs be included in MER?
It depends on the selected definition. This guide uses total marketing expense and requires that scope to be documented. Do not compare a media-only ratio with a broader-cost MER without explaining the difference.
Can we add revenue from advertising platforms?
One sale can be credited by several platforms. Inspect attribution and duplication risk before treating the sum as store revenue. Keep channel reporting separate from the business’s total-revenue record rather than combine them uncritically.
Is there a good CAC or MER target for every brand?
There is no universal target. Contribution, repeat purchase, market, growth stage and cost scope vary. Do not use another example as a spending threshold without validating the business’s own financial and operational conditions.
Should we raise spend when the ratios look good?
A ratio alone is insufficient. Review data quality, new-customer suitability, contribution, stock and cash planning together. Test the effect of a defined change rather than assume a historical ratio will remain unchanged at a higher spend level.
LET’S DEFINE THE SCOPE
Clarify the definitions behind the growth report
Share revenue and cost scope, advertising reports and customer definitions. We can connect the ratios to a comparable decision record.
Review marketing measurement