Google Ads exposes dozens of metrics, and most e-commerce operators track the wrong ones — or track the right ones without knowing what each is actually for. The distinction that matters isn’t which metrics are “good,” it’s which ones drive a decision versus which ones explain why a decision metric moved.

This guide sorts paid search KPIs into those two categories, plus a third one worth ignoring, and covers how the right set changes as your spend grows.

Tier 1: The decision KPIs

ROAS, against your breakeven

Return on ad spend is the headline number, but it’s meaningless in isolation. A ROAS of 4 is excellent at 60% gross margin and loss-making at 20%. Calculate your breakeven ROAS (1 ÷ gross margin) and treat that as the line — everything above it contributes, everything below it costs you money regardless of how healthy the raw number looks.

One structural caveat: the ROAS Google Ads reports uses its own attribution window (30 days by default, configurable) and its own conversion counting. That won’t match what GA4 or your Shopify numbers say — we cover why in our guide on attribution mismatches.

CPA against average order value

Cost per acquisition only means something next to what a customer is worth. Two campaigns with identical ROAS can have wildly different CPAs and average order values — and the one with a lower CPA on cheaper products may be far more scalable.

Impression share

The percentage of available impressions you actually captured. This is the most under-used decision metric in paid search: a high-ROAS campaign with low impression share is leaving money on the table. It tells you that demand exists which your budget isn’t capturing, which is the clearest possible signal to increase spend.

Look at the two loss reasons Google reports separately: impression share lost to budget (raise the budget) versus lost to rank (improve ad relevance, bids, or Quality Score).

Tier 2: The diagnostic KPIs

These don’t drive budget decisions directly, but they explain why the Tier 1 numbers moved.

Quality Score

Google’s rating of ad relevance, expected CTR, and landing page experience. A low Quality Score inflates your CPC at equal position — it’s frequently the hidden cause behind a CPA that climbs with no obvious explanation.

Don’t optimize for the score itself. Optimize the alignment it measures: does the keyword match the ad copy, and does the ad copy match what’s actually on the landing page? Fix that and the score follows.

Search terms report

The actual queries that triggered your ads, as opposed to the keywords you bid on. This is where budget quietly leaks — broad and phrase match keywords pull in queries that will never convert. Reviewing this report and adding negative keywords is often the single highest-return hour you can spend on a search account.

Note that this report isn’t available through the native Looker Studio connector, as we mention in our Google Ads connector guide — you’ll need to check it in the interface.

Conversion rate by ad group

Not just at campaign level. Uneven conversion rates across ad groups point to a mismatch between what people searched for and where they landed — usually fixable by tightening the keyword-to-landing-page relationship rather than by adjusting bids.

CTR

Useful as a relative signal within a campaign, but be careful comparing across campaign types or match types: branded keywords naturally have far higher CTR than generic ones, so an account-wide CTR average tells you almost nothing.

Tier 3: Metrics to deprioritize

Raw impressions — volume without context. Impression share is the useful version.

Average position — Google deprecated this metric in favor of impression share metrics for good reason: position told you where you appeared, not whether you were appearing often enough.

Clicks in isolation — a metric that goes up when you spend more. Meaningful only alongside cost and conversion data.

How the right set changes with spend

Under $1,000/month: ROAS, CPA, conversion rate. At this level Google’s algorithms don’t have enough conversion volume to optimize finely, and neither do you — additional metrics add noise, not insight.

$1,000-$10,000/month: add impression share and the search terms report. This is the range where wasted spend on irrelevant queries becomes material money, and where budget-constrained campaigns start costing you real revenue.

Above $10,000/month: add Quality Score monitoring and ad-group-level conversion rate analysis. At this spend, small structural inefficiencies compound quickly, and the speed at which you spot them directly affects how much budget gets wasted.

Where to track them

The Google Ads interface handles day-to-day campaign work well. A dashboard becomes necessary when you want to cross Google Ads spend against real Shopify revenue rather than platform-reported conversions — the multi-source structure we cover in our Looker Studio dashboard guide.

For campaign-type-specific guidance (Search vs Shopping vs Performance Max), see our breakdown of Google Ads KPIs for Shopify.

FAQ

What’s the difference between paid search KPIs and general PPC KPIs? Paid search covers keyword-driven campaigns where the user has expressed intent through a query. That intent changes which metrics matter: impression share and Quality Score are central to search, but meaningless for display or social campaigns where there’s no query to match against.

Is a high Quality Score worth optimizing for directly? Not as a goal in itself. Quality Score is a diagnostic — it tells you whether your ad, keyword and landing page align. Improving that alignment lowers your CPC, which is the actual benefit. Chasing the score itself, rather than the alignment behind it, is optimizing the thermometer instead of the temperature.

How often should I review paid search KPIs? Weekly for budget and campaign-level decisions, and monthly for structural ones (account structure, keyword strategy). Daily checking on most accounts produces noise rather than signal — conversion data needs volume to be meaningful, and Google Ads backfills conversions to the click date for days afterward.

Want a dashboard that ties your paid search performance to real Shopify revenue instead of platform-reported conversions? Check out our Shopify Dashboards offer or book a free 30-minute call.