Shopify Ad Metrics: ROAS, MER and CAC You Can Trust
Shopify ad metrics you can trust start with five numbers: ROAS as the ad platform reports it, ROAS from Shopify’s own attribution, MER (total revenue over total ad spend), customer acquisition cost and payback time. The first is the one every ad dashboard shows and the one most likely to be too high, because each platform credits itself. The other four come from your Shopify admin and your ad bills, and when they agree, you can believe the result.
Five metrics
| Metric | Formula | Where the numbers come from |
|---|---|---|
| Platform ROAS | Revenue the platform attributes to its ads ÷ spend on that platform | Meta Ads Manager, Google Ads |
| Shopify ROAS | Sales Shopify attributes to the channel ÷ spend on that channel | Analytics > Reports > Performance by marketing channel, which also shows ad spend, ROAS, CPA and CAC for connected ad platforms; for others, the ad bill |
| MER (marketing efficiency ratio) | Total sales ÷ total ad spend across all platforms | Total sales from Shopify’s Analytics, spend from every ad bill |
| CAC (customer acquisition cost) | Total ad spend ÷ new customers in the period | New customers over time report for the count |
| Payback | CAC ÷ gross profit per customer per month | Your margins and the Returning customers report |
A worked month: a store spends $3,000 on Meta and $1,000 on Google. Meta reports $15,000 in purchases (ROAS 5), Google $4,000 (ROAS 4). Shopify’s total sales for the month are $14,000, and its Performance by marketing channel report credits $7,500 to Meta and $3,000 to Google. Shopify ROAS is 2.5 for Meta and 3 for Google, and MER is $14,000 ÷ $4,000 = 3.5. The platforms together claim $19,000 of a $14,000 month, which cannot all be true. If 160 of the month’s customers were new, CAC is $4,000 ÷ 160 = $25. With $10 of gross profit per customer per month, the payback is two and a half months.
MER cannot be gamed by any one platform, because it uses the sales you actually banked. Watch it month by month: if spend rises and MER holds, the extra spend is working, whatever each dashboard says.
Why ad platforms and Shopify disagree
Each platform counts conversions by its own rules and gives itself the credit for any sale it touched. A customer who saw a Meta ad, clicked a Google ad a week later and bought from an email can be counted by all three. Shopify instead gives each order to referrers it can see, by the model you choose.
Shopify’s marketing reports page, read on October 23, 2026, lists the models:
| Model | Credit |
|---|---|
| Last non-direct click (the default) | 100% to the last channel before the purchase, ignoring direct visits |
| Last click | 100% to the last channel, including direct visits |
| First click | 100% to the first channel, including direct visits |
| Any click | 100% to every channel the customer clicked |
| Linear | Equal credit to each click in the journey |
Shopify notes that Any click gives out more credit than the orders you received, and suggests it for analyzing one channel or for reconciling with what each channel reports. That is the closest Shopify view to how a platform counts. Two more rules from the same page matter: a first-interaction referrer resets if a visitor does not buy within 30 days, and after an order, the next referrer counts as the first interaction for the next order. Sessions also changed in September 2026, when Shopify rolled out a new session measurement from 21 to September 23; compare conversion rates on either side of that week with care.
Use Shopify’s attribution and UTMs
Shopify can only credit what it can see, so make every ad link visible to it.
- Tag every ad link with UTM parameters, lowercase and consistent:
utm_source=facebook&utm_medium=paid&utm_campaign=202611-winter-sale. Shopify’s marketing performance page says traffic withutm_campaignin the URL is attributed to marketing. - Read the results on the Growth page for campaigns created in Shopify, and in Analytics > Reports for all traffic. The Performance by marketing channel report puts paid and organic channels in one table, with the attribution model menu in its settings.
- Ask Sidekick for a quick cut, such as “Show sessions and net sales by UTM campaign for last month”. Shopify says Sidekick can group marketing data by UTM campaign, source, medium or referrer, but cannot compare attribution models.
- Allow for the delay. Shopify’s Growth page notes that its marketing metrics can take up to 24 hours to update.
We run our own app marketing the same way: every link to an app listing carries UTM parameters, and installs are checked against the partner data rather than against the clicks a platform reports. The habit costs a minute per link and is what makes the Shopify ROAS row above possible.
The AI campaign types themselves are in AI advertising for Shopify, a dashboard that puts these numbers on one screen in KPI dashboard, and the reports in general in Shopify analytics. The Shopify marketing hub collects the channel guides, and the running a store hub the reports and operations side.
Frequently asked questions
What is a good ROAS? A good ROAS is one above your break-even point, which depends on your margin: with a 40% gross margin, you need a ROAS of 2.5 on Shopify-attributed sales just to cover the ad spend. Judge it on Shopify’s numbers, not the platform’s.
Why is Meta ROAS higher than Shopify? Meta credits a purchase to its ads by its own rules, including people who saw an ad and bought later through another channel. Shopify’s default model gives each order to the last non-direct click it can see, so a sale that Meta and an email both touched is counted once, for the email.
What is MER? MER, the marketing efficiency ratio, is total sales divided by total ad spend across all platforms. It ignores who gets the credit, which makes it the number to watch when platform reports disagree.