What's a good MER or blended ROAS to aim for in a post-iOS14 world?

TL;DR

Your ideal ROAS target is calculated from your unique margins, not from industry benchmarks.

Chasing too high a ROAS (e.g., 4x instead of an optimal 3x) leaves profit on the table.

Over-efficiency is often a symptom of underspending and can stunt your business's growth.

Use incrementality testing to find your true, profit-maximizing return on ad spend.

A good ROAS is a floor for profitability, not a ceiling for efficiency.

Tony Chopp made a point on Ecommerce Playbook that completely reframes your question: “4 is not necessarily better than 3.” What he means is that if your specific unit economics show that a 3x ROAS maximizes your total profit, then chasing an "efficient" 4x ROAS is a losing strategy. You'll hit that 4x by spending less and targeting a smaller, higher-intent audience, but you’ll leave a huge amount of volume, customers, and gross profit on the table. Efficiency feels good, but it's often a sign of underspending. Over-efficiency is a symptom of leaving growth behind.

The hosts of The Bottom Line and Ecommerce Playbook repeatedly say that your ROAS target shouldn’t come from vibes or industry benchmarks. It must be calculated from your business's specific contribution margin and goals. As they stress on The Bottom Line, your "ROAS target should vary dramatically based on your business goals." The question isn’t “what’s a good ROAS?” but rather, “what’s the lowest ROAS I can profitably sustain to acquire a new customer?” This number is your floor. As long as you're above it, you can spend more to grow faster.

Chasing an arbitrarily high number is dangerous. Chad Rubin talked about this on the Up Arrow Podcast, calling it the "ROAS death spiral." It happens when brands get spooked by rising ad costs and demand higher and higher efficiency, forcing them to cut spend, which suffocates growth. Similarly, on Future Commerce, Kiri Masters called ROAS a "terrible metric" for growth because it inherently limits how much you can spend.

While a blended metric like Marketing Efficiency Ratio (MER) is a better North Star than platform ROAS, it can still hide underlying problems. The key is to understand what ROAS you actually need to be profitable, and then use that as a guide to scale your ad spend. Taylor Holiday gave a great practical example on Ecommerce Playbook of setting a lower ROAS target inside the ad platform than your actual goal, because incrementality testing shows the platform underreports its true impact. Your goal isn't to find a "good" ROAS. It's to find your ROAS.