Also calledReturn on investmentExhibitor ROIEvent return
The organizer's calculation
Revenue is straightforward: tickets, square metres, sponsorship and add-ons. The cost side is where editions get compared badly, because venue, build, marketing and staff are often tracked in different places. Held consistently, the useful figures are revenue per square metre, revenue per attendee and cost per registration.
The exhibitor's calculation
Leads scanned, qualified by whatever grading they applied at the stand, multiplied by their own conversion rate and average deal size, against the all-in cost of the stand including build and staff travel. The organizer supplies the first half; the exhibitor supplies the second. Giving them the first half on the last day is what makes the conversation possible.
What to collect so the number exists
Verified attendance rather than registrations, scans by stand, dwell by zone, session attendance, and revenue attributed to the edition rather than the calendar year. Collected as the show runs, these produce the report automatically; collected afterwards, they produce an argument.