The essentials
- The principle: impact is measured by the gap between what happened and what would have happened without the campaign; you therefore need a baseline (a period, an area or a control group).
- Four methods: direct attribution for digital, before-and-after corrected for seasonality, an area or control group, and an awareness survey.
- Free metrics: brand searches (Search Console, Google Trends), direct traffic, calls and directions on the Google listing, mentions and followers.
- The rule: decide the metrics and take the baseline before the launch, never after.
An outdoor campaign, a radio spot, a partnership, a trade show, a social campaign: how do you know what it produced? The difficulty isn't a lack of data but the absence of a baseline. Measuring impact always comes back to comparing what happened with an estimate of what would have happened without the campaign. This article presents the four methods usable in 2026 by channel, the metrics to take and a complete worked example.
Before launching: set the baseline
Any impact measurement starts before the campaign. Three things are to be fixed in writing: the objective (awareness, traffic, enquiries, sales), the metrics that reflect it, and their baseline level over the previous 8 to 12 weeks, allowing for last year's seasonality. Without that baseline, any figure taken afterwards can be read any way you like. You also have to plan the measurement window: the effect of an awareness campaign reads over 4 to 12 weeks, that of a promotion over the offer's duration plus a week.
The four measurement methods
| Method | Principle | Suited to | Limit |
|---|---|---|---|
| Direct attribution | A link, UTMs, a promo code, a dedicated number, a landing page specific to the campaign | Digital, email, print with a QR code or a short URL | Doesn't capture the indirect effect (the person who searches for the brand later) |
| Corrected before-and-after | Comparing the campaign period with the baseline, corrected for the trend and last year's seasonality | Any campaign, particularly local and offline | An outside event (a competitor, the weather, the news) can distort the reading |
| An area or control group | Running in one area or segment and comparing with an equivalent unexposed one | Outdoor, radio, leafleting, networks of locations | Requires two comparable areas and enough volume |
| An awareness survey | Questioning a sample before and after on brand awareness and image | Large-scale brand campaigns | Costs €2,000 to €15,000 depending on the sample; poorly suited to a small business |
For a small business, the first two methods cover most cases, with the third added for a network. Setting up the tracking links and parameters is described in tagging your digital campaigns.
The metrics that reflect impact
- Brand searches: impressions and clicks on the queries containing the company name in Search Console, the Google Trends curve. It is the best free awareness signal: an effective campaign lifts those searches within the week.
- Direct and brand traffic: "direct" and brand organic sessions in GA4, isolated with a segment.
- The Google listing: searches for the listing by name, calls, directions; a local campaign's effect shows there within days. See the Google listing's performance.
- Enquiries and sales: forms, calls, orders, with the source declared ("how did you hear about us?" is still a useful question).
- Social signals: followers, mentions, profile visits; secondary but quick to take.
The metrics to set aside: impressions and "contacts" reported by the media owner, theoretical reach, a video's view count with no duration. They measure distribution, not impact. The distinction is developed in vanity KPIs.
A worked example: a local outdoor campaign
A renovation company invests €6,000 in 4 weeks of outdoor advertising across a conurbation, with a dedicated short URL and a tracking number. Baseline: the 8 weeks before, corrected for the same period last year (+5% of trend).
| Metric | Weekly baseline | During and 4 weeks after | Attributable gap |
|---|---|---|---|
| Brand searches (Search Console) | 210 impressions | 390 impressions | +86%, of which +5% trend: around +80% |
| Visits through the dedicated URL | 0 | 95 over 8 weeks | 95 visits attributed directly |
| Calls from the Google listing | 18 a week | 29 a week | +60%, or 85 extra calls over 8 weeks |
| Quote requests (all sources) | 11 a week | 16 a week | +40%, or 40 extra quotes |
| Quotes signed (30% rate, €3,500 order value) | 12 jobs | €42,000 of revenue, 30% margin: €12,600 |
Direct attribution (95 visits) massively understates the effect; it is the corrected before-and-after on brand searches and calls that gives the real measure. The return on investment is calculated on the margin: €12,600 for €6,000 invested, an ROI of 110%. The formula and its variants are in calculating your marketing ROI.
The most frequent traps of interpretation
- Comparing with the previous month in a seasonal business: compare with the same period last year.
- Stopping the measurement when the campaign ends: part of the effect arrives in the following 2 to 4 weeks.
- Attributing the whole gap to the campaign when a competitor has closed, a Google Ads campaign was launched at the same time or the weather changed. Isolate the other known variations.
- Counting only direct attribution: promo codes and dedicated URLs capture 10 to 30% of an offline campaign's real effect.
How GreenRed helps
Rather than juggling several tools, GreenRed's return on investment module brings these metrics together in a single dashboard, compares them over time and tells you which actions come first. You can try it free, with no card, from the Pricing.
Frequently asked questions
How do you measure the impact of a radio spot or a poster with no clickable link?
Through before-and-after on brand searches, direct traffic, calls and directions from the Google listing, corrected for seasonality. Add a memorable short URL or a promo code to capture a direct share, knowing it represents only a fraction of the total effect.
How long after the campaign should you measure?
Take the metrics during the campaign and for 4 weeks after for an awareness campaign, one week after for a dated promotion. Beyond that, the effect dissolves into the noise and other marketing actions blur the reading.
Can you measure the impact of a trade show or an event?
Yes, with three readings: the contacts collected on site and what becomes of them in the CRM over 6 months, the rise in brand searches and direct traffic in the week of the event, and the meetings obtained. The full cost (stand, time, travel) is compared with the margin of the business signed.
What if the volumes are too low to conclude?
With fewer than 30 enquiries a month, weekly variations are noise. Lengthen the measurement window, aggregate across several similar campaigns, and favour the higher-volume metrics such as brand searches or visits, which move before the enquiries do.