In one sentence
Return on ad spend is the revenue you earn for every dollar spent on ads, found by dividing ad revenue by ad cost, and it tells you which campaigns pay for themselves.
How to calculate ROAS
Divide revenue from an ad campaign by what you spent on it. Spend $1,000 and earn $4,000 and your ROAS is 4, often written as 4:1 or 400%.
The revenue side depends on attribution: which sales your ad platform or analytics credits to the ad. Different tools credit differently, so the same campaign can show a different ROAS in each.
ROAS vs. MER vs. ROI: which number to trust
- Formula · ROAS: Ad revenue ÷ ad spend · MER: Total revenue ÷ total marketing spend · ROI: Profit ÷ total cost
- Scope · ROAS: One campaign or channel · MER: The whole store · ROI: Any investment
- Accounts for costs beyond ads? · ROAS: No · MER: Marketing costs only · ROI: Yes
- Best for · ROAS: Comparing campaigns · MER: Checking if marketing works overall · ROI: Judging real profit
Why ROAS matters for ecommerce brands
ROAS is the fastest way to see which ads earn their keep and which ones to cut. But revenue isn't profit. A campaign can show a strong ROAS and still lose money once product, shipping and fees come out.
Work out your break-even ROAS first: divide 1 by your gross margin. At a 40% margin, you need a ROAS of 2.5 just to cover product costs on ad-driven orders.
How to improve ROAS on your store
- Cut the campaigns, audiences and placements below your break-even ROAS.
- Send ad traffic to the most relevant page: a specific product or category, not your homepage.
- Raise conversion rate and average order value (AOV), so the same clicks earn more.
- Check marketing efficiency ratio (MER) alongside ROAS, since platforms can take credit for sales that would have happened anyway.
ROAS FAQs
What's a good ROAS for an online store?
Any ROAS above your break-even point is profitable on first orders. Your break-even depends on your margin, so a good ROAS for one store can lose money for another.
Why does my ROAS differ between my ad platform and my store analytics?
Each tool uses its own attribution window and rules. An ad platform may credit a sale to someone who saw an ad days ago, while your store analytics credits the last click. Pick one source of truth and use it consistently.
Should I include repeat purchases when judging ROAS?
For a store with strong repeat buying, yes. First-order ROAS can look weak for a customer who comes back many times. Compare customer lifetime value (LTV) with customer acquisition cost (CAC) for the full picture.
About the author
Jenn Starr, Co-founder, Selix
Jenn has spent 20+ years helping SaaS startups build their marketing and implementation playbooks. She has bootstrapped three marketing agencies and is a 500 Startups alum. At Selix, she leads the work of getting ecommerce brands named in AI answers.
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