ROAS — return on ad spend — is the metric every performance marketer knows. But it's also the metric that most often misleads them.
The problem with ROAS
ROAS measures revenue generated per dollar of ad spend on a specific channel. It sounds clean. But it ignores everything else:
- Organic traffic that would have converted anyway
- Brand halo effects across channels
- Incrementality — did the ad actually cause the sale?
A campaign can show 4x ROAS and still be losing money if it's cannibalising organic conversions.
What MER tells you instead
Marketing Efficiency Ratio (MER) is total revenue divided by total marketing spend — across all channels. No attribution model. No last-click bias.
MER = Total Revenue / Total Marketing Spend
If you spend $50,000 across all channels and generate $200,000 in revenue, your MER is 4.
It's blunt. But it's honest.
When to use each
Use ROAS for: channel-level optimisation, creative testing, bid strategy decisions.
Use MER for: budget allocation across channels, monthly performance reviews, presenting to the board.
The mistake is using ROAS where you should be using MER. ROAS will always flatter your best-attributed channel. MER tells you the real picture.
How ClickBoss tracks both
ClickBoss shows both MER and ROAS in your morning briefing and metrics snapshot. When your MER drops but your ROAS holds flat, that's usually a signal that incrementality is declining — and ClickBoss will flag it.