Influencer marketing: KPIs and metrics for measuring a campaign

As we saw in the previous article in our series on influencer marketing, this practice can be of great value within digital marketing. Yet using it indiscriminately carries clear risks: and more and more people are now realising it.

That is also why using clear KPIs when assessing a collaboration with an influencer is extremely important: it establishes which clear objectives to pursue and sets explicit goals for the collaboration.  

Influencer marketing KPIs are the indicators chosen to verify whether a collaboration with a creator has actually produced the expected effect. Among them we consider qualified reach, attention, traffic, sales and brand value. A metric describes what happened; a KPI links the data to a decision.

Measuring means linking investment to business results. In this article we explore the topic in depth, to measure the reach, engagement, conversions, ROAS and ROI of influencer campaigns.

The objective comes before the KPIs

Awareness and sales use the same creators, but require different criteria. In the first case the aim is to reach new people who fit the target; in the second, to generate purchases or leads at a sustainable cost. Judging a launch on revenue alone underestimates its role; assessing a performance campaign on impressions sidesteps the economic question.

An effective system distinguishes a primary KPI, which defines success; a control KPI, which protects margin, quality or reputation; and diagnostic metrics, which explain the result. For an e-commerce business, CPA can be the primary KPI and margin per new customer the control.

Influencer marketing KPIs by objective

The table links objectives to indicators, avoiding reports full of numbers but lacking priorities.

Reach indicates unique users; impressions count every exposure; frequency links the two values. Definitions can vary across platforms and the data cannot always be added together, as shown by the TikTok Ads glossary and the IAB report on the creator economy.

Engagement rate: the denominator changes the meaning

Engagement rate has no single formula. Interactions divided by followers measure the long-standing relationship with the community; divided by reach, they indicate the response of the people exposed; divided by impressions, they relate actions to all views. Percentages with different denominators are not comparable.

For a published campaign, the most informative formula is often:

Engagement rate by reach = relevant interactions / reach × 100

The numerator matters too. Shares, saves and comments express different intentions and should be read qualitatively, not simply added up. It is the same distinction we discussed in our guide to engagement and how to measure it.

For video, watch time and completions describe attention better than views alone; on YouTube, not all views come from thumbnail impressions.

CPA, ROAS and ROI answer different questions

CPA shows what a conversion cost. ROAS compares attributed revenue with spend. ROI checks whether the initiative created value after costs and should use profit or margin, not revenue alone.

CPA = total cost / attributed conversions

ROAS = attributed revenue / investment

ROI = (profit generated – total cost) / total cost × 100

Hypothetical example: a campaign costs 18,000 euros and generates 42,000 euros in revenue, so the ROAS is 2.33. With a 55% margin, the ROI is roughly 28.3%. The two metrics do not tell the same story about profitability.

Total cost includes fees, gifting, shipping, production, agency fees, paid amplification, tools, usage rights and internal time. Leaving them out distorts the comparison with other channels.

Tracking is designed before go-live

Attribution cannot be reconstructed accurately once a campaign has ended. Before publication you need consistent UTMs, an identifier for each creator and piece of content, unique codes, verified conversion events and an agreed time window. Google recommends standard naming for source, medium, campaign and content (see the GA4 guide to custom URLs).

Each source sees only part of the journey:

The contract should set out the data, format, deadline and observation period. Otherwise the report relies on inconsistent screenshots, a fragmentation that IAB considers structural.

Attribution and incrementality are not the same

Attribution assigns credit to the observed touchpoints. Incrementality estimates how many conversions would not have happened without the campaign. A code used in 300 orders shows an association, but does not prove that every purchase is new or caused by the creator.

GA4 distributes credit according to different models, but no model removes the limits of the data or replaces an experiment. The Google Analytics documentation explains how credit is assigned along the paths.

Where scale allows, the most robust method compares exposed and control groups, or equivalent areas or periods. In smaller projects, UTMs, codes, branded search, direct traffic, new customers, post-purchase surveys and the previous baseline are triangulated. The result should be presented together with its level of certainty.

Earned media value assigns a theoretical value to visibility, but does not prove sales, brand lift or causal uplift. IAB regards it as a directional indicator, not a financial outcome metric.

Comparing creators and turning the report into decisions

The ranking must not automatically reward whoever generates the most volume. Results need to be normalised for cost, actual reach, platform, format, duration and audience quality. Reels, Stories and YouTube videos have different life cycles; comparing them only over the first 24 hours favours the faster formats.

The median of previous performance reduces the effect of viral peaks. In multi-creator campaigns, adding up individual reach figures can overstate the number of people reached.

If the brand acquires rights for advertising or owned channels, the report must separate the performance of the publication from its future usage value, as we anticipated in our article on content creation as a measurable and reusable process.

The first page should show the objective, primary KPI, result, investment, baseline and recommendation. There are three questions: what to scale, what to adjust and what to stop? A low CPM with negative sentiment is not efficiency; many visits and few conversions may signal a mismatch between the promise and the landing page.

New Connections (FAQ)

What is the most important KPI in an influencer marketing campaign?

No single KPI is valid for every campaign. It depends on the objective: qualified reach and brand lift make sense for awareness, CPA and conversion rate for acquisition, ROAS and margin for profitability. The choice should be made before selecting creators, because it also determines which data to collect and how to assess the result.

How can you tell whether sales generated by an influencer would have happened anyway?

UTMs, discount codes and attribution platforms show which conversions can be associated with the creator, but on their own they do not prove that the collaboration caused them. Getting closer to incrementality requires comparisons with previous baselines, control groups, unexposed areas or other signals such as growth in branded searches and new customers. The difference matters: attributing a sale means knowing which route it took; measuring incrementality means understanding whether that sale would exist without the campaign.

When does an influencer campaign need more structured measurement?

As investment, the number of creators and the touchpoints involved increase, relying on insights from individual platforms is no longer enough. A common structure is needed that links costs, reach, traffic, conversions, margins and brand outcomes, keeping data from different sources comparable. This is the level at which Bliss can work in designing and evaluating campaigns: defining objectives and KPIs up front, building the tracking system and turning the final report into decisions on which creators to scale, which to adjust and which collaborations to end.

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