Essential digital advertising metrics

CTR measures the percentage of people who click on your ad relative to those who see it. It’s calculated as clicks ÷ impressions × 100. It’s the primary indicator of your ad’s relevance to the audience: a high CTR means your message resonates.

CTR benchmarks vary enormously by platform and format. On Google Search, a 3–5% CTR is acceptable and above 7% is excellent. On Display, 0.5% is normal. On Facebook/Instagram feed, 1–2% is standard. Always compare against your own history and your sector’s benchmarks.

CPC measures how much you pay for each click on your ad. CPM measures how much you pay per thousand impressions. They’re operational efficiency metrics: a low CPC means you’re attracting clicks efficiently, but it says nothing about whether those clicks convert.

In search campaigns (Google Ads), CPC is the standard payment model and varies by keyword competition. In awareness campaigns (Display, Video), CPM is more relevant because the goal is maximising reach, not clicks.

CPA measures how much it costs you to achieve a conversion: a lead, a sale, a download or any action you define as an objective. It’s the most direct business metric because it connects ad spend with actual results.

For CPA to be useful, the definition of “conversion” must be rigorous. A lead who fills in a form is not the same as a qualified lead who moves to sales. Distinguish between lead CPA (form), MQL CPA (marketing qualified lead) and customer CPA for a complete picture.

ROAS measures the revenue generated per euro invested in advertising. A ROAS of 5 means that for every euro spent, you recover five euros in revenue. It’s the go-to metric for ecommerce and any business that can track direct revenue from campaigns.

The minimum profitable ROAS depends on your margins. If your gross margin is 50%, you need a ROAS of at least 2 to cover product cost and advertising. If your margin is 30%, you need a minimum ROAS of 3.3. Always calculate your break-even ROAS before launching campaigns.

Impression share measures what percentage of available impressions for your keywords you’re capturing. If your impression share is 60%, you’re missing 40% of opportunities. Google breaks down lost impressions by budget and by rank.

Impressions lost to budget indicate you need more investment to cover all demand. Impressions lost to rank indicate your Quality Score or bid is insufficient. Each cause requires a different action.

Google Ads’ Quality Score (1–10) reflects ad relevance, landing page experience and expected CTR. It’s not a result metric but a diagnostic one: it indicates the health of the keyword–ad–landing relationship.

A QS below 5 signals a serious problem that inflates every click’s cost. Keywords with a QS of 7 or above are the most efficient. Prioritise improving QS on keywords with the highest spend volume, as CPC savings have the greatest absolute impact.

Metrics should never be read in isolation. A high CTR with a high CPA means the ad attracts clicks but the landing page doesn’t convert. A low CPC with low impression share means you’re paying little but reaching few people. Performance is evaluated by combining operational and business metrics.

Set up a dashboard with key metrics organised by level: operational (CTR, CPC, CPM), tactical (CPA, conversion rate, impression share) and strategic (ROAS, ROI, cost per customer). Review operational metrics daily, tactical ones weekly and strategic ones monthly.