Recommended resources
The freely available resources this lesson will direct you to.
Hello! In the previous lesson, you turned a storefront manager’s concern about a mobile banner into a measurable question: did the share of US mobile product-page sessions that placed an order change after launch? Now we need to make that measurement repeatable. If two analysts calculate “purchase rate” differently, their charts may disagree even when they use the same data.
This lesson shows how to write a short KPI definition that fixes the formula, scope, time period, and decision use before reporting a number. We’ll return to the banner decision and build a definition someone else could use. Allow about 40 minutes, including the short resources and a practical drafting pass.
A KPI is a measure selected for a decision
A metric is something you can measure. A key performance indicator (KPI) is a measure selected to track progress toward a particular goal and inform a decision. “Mobile orders” is a useful metric; it becomes a KPI for this manager only if you establish what goal it monitors and how its value will influence the keep-or-remove discussion.
Watch these short portions of What Are KPIs? 5 TOP TIPS For Defining YOURS by Adam Finer – Learn BI. They connect business goals to reporting periods and measurement boundaries.
What Are KPIs? 5 TOP TIPS For Defining YOURS. BI For Beginners
Adam Finer – Learn BI introduces KPIs and shows why both reporting periods and filters matter when defining them.
Watch the definition, then periodicity and focused KPIs. Notice how “website performance” becomes more useful when the period and the part of the business being measured are specified.
The key word is selected. You could track visits, orders, revenue, and many other numbers for the banner. The primary KPI should reflect the concern the manager confirmed: whether product-page visitors are less likely to buy. Orders and revenue can remain supporting measures; they need not all become headline KPIs.
For a concise account of the difference, read the indicated portions of KPIs in a company: how to measure performance and decide faster from BR Solutions.
KPIs in a company: how to measure performance and decide faster
Read how the article distinguishes a performance measure from a KPI, then use its questions to connect a KPI to an owner and a decision.
In “What a KPI is,” read the distinction from the opening definition through the test of whether a number helps someone act. Then, in “Choosing KPIs for different types of company,” start after the paragraph warning against a universal KPI list. Read the guiding questions through the final question about where the event is recorded. Focus on who decides, how soon, and from which records.
Fix the formula before looking at the result
For the banner, call the proposed KPI US mobile product-page session purchase rate. Its formula is:
“Eligible” must mean the same thing in both parts of the fraction. Here, an eligible session is a US-store mobile session that viewed a product page. A session with two orders contributes one to the numerator, because this KPI asks what share of sessions included a purchase—not how many orders occurred per session. A session that purchased but never viewed a product page is outside both counts.
This distinction matters even if the dashboard displays only one percentage. One analyst might count orders divided by product-page views; another might count purchasing sessions divided by product-page sessions. Those formulas answer different questions. A good definition names the numerator, denominator, unit (percent), and counting rule clearly enough to expose the difference.
Not every KPI is a rate: total completed orders per week can also be a KPI if that count is central to a goal and decision. For a rate, however, the denominator deserves particular care. It determines who had the opportunity to appear in the numerator.
Set the boundary and the clock
The scope states what belongs in the calculation. Our proposed boundary is the US store, mobile devices, and sessions that viewed a product page. It also states what is excluded: desktop sessions, other stores, and sessions without a product-page view. The team should agree on how its analytics system classifies a session as mobile and a page as a product page, then apply those rules consistently.
The time period answers more than “weekly.” For this decision, report separate values for March 1–7 and March 8–14, 2026, assigning a session to a week by its start date in the store’s agreed reporting time zone. The banner launched at the start of March 8, so these are the before and after weeks specified in the previous lesson. State when data is ready to report as well: an incomplete final day could make the second week appear worse simply because some records have not arrived.
The formula is only feasible if you can identify eligible sessions and link their orders to those same sessions. Shopify order totals alone would not establish that link. If the available systems cannot make it reliably, do not silently substitute orders divided by visits and keep the same KPI name. Flag the limitation and agree on a different measure.
A written definition prevents such substitutions from being invisible. Return to the BR Solutions article for its compact definition-card checklist.
KPIs in a company: how to measure performance and decide faster
Use the definition-card table as a model for documenting a calculation that others can repeat.
In “How to calculate KPIs so that they count the same way everywhere,” read the card guidance, including the table from “Name” through “Change history.” Focus first on management purpose, formula, scope, and period; then notice how source, owner, exceptions, and changes protect comparisons over time.
The following example sheet uses a different operational KPI—on time in full (OTIF) delivery—to show how those elements fit together. Its boundaries specify which orders count, while its data-governance section records where the figures come from.
Put the storefront KPI on one card
Here is a workable draft definition, subject to the manager confirming the business rules and the data team verifying the records:
| Field | Draft definition |
|---|---|
| Name and purpose | US mobile product-page session purchase rate; monitor purchasing among the sessions relevant to the banner decision. |
| Formula | Eligible sessions with at least one same-session order ÷ all eligible sessions, multiplied by . Count each session once in each applicable count. |
| Scope | US-store mobile sessions that viewed at least one product page; exclude other stores, desktop sessions, and sessions without a product-page view. |
| Period | Weekly, by session start date in the agreed store reporting time zone. Compare March 1–7 with March 8–14, 2026; report after both weeks’ records are complete. |
| Source and check | Session/page-view records and order records linkable by session. Confirm link coverage and consistent tracking across both weeks before publishing the rate. |
| Decision use | Inform the manager’s keep-or-remove review. If the rate declines, examine traffic mix, order and revenue totals, and tracking changes before recommending action. |
Suppose the verified counts were 84 purchasing sessions out of 2,000 eligible sessions before launch and 72 out of 2,000 after launch. The reported rates would be and , respectively. Because the denominator and scope are defined, another analyst can reproduce those figures and investigate the difference.
The card does not claim that the banner caused the difference. Nor should an analyst invent a success target after seeing the result. If the manager has an agreed target or alert threshold, document its value, effective date, and what happens when it is missed. A threshold might trigger investigation; it need not automatically trigger removal of the banner.
A brief drafting pass
Spend about 8–10 minutes making your own copy of the card for the Unbounce landing-page question from the previous lesson. Use the same six fields, but define a successful form-submission rate per landing-page visit, comparing April 27–May 3 with May 4–10. Leave any unknown rule—such as whether multiple submissions during one visit count once—as “confirm with owner” rather than guessing. This is a definition draft, not a calculation: its purpose is to make disagreements visible before you build a report.
When reviewing it, pay particular attention to whether a visit eligible for the numerator is also eligible for the denominator, and whether the decision owner would know what to do with the reported value. Those two checks catch many polished-looking but unusable KPIs.
Key takeaways
A defensible KPI connects a goal and decision to a repeatable measurement. Specify its numerator and denominator or other calculation, its inclusion and exclusion rules, the dates and reporting cadence, and how the decision owner will use it. Record the source and unresolved data checks so a precise-looking number does not conceal a measurement problem.
Next, we’ll look more closely at a dataset itself: what does one row represent? That observation grain will determine whether the counts in a KPI like this one are valid.