Impressions equal reach multiplied by average frequency, so frequency equals impressions divided by reach and reach equals impressions divided by frequency. 1,000,000 impressions reaching 250,000 people is a frequency of 4. GRPs equal reach percentage multiplied by frequency: 25 percent reach at a frequency of 4 is 100 GRPs.
What moves it
Reach requires recognizing the same person across exposures, which platforms do within their own walls and estimate across them. Cross-platform reach is deduplicated with a panel or identity graph or it is overstated.
Run your own numbers with the Reach and frequency calculator.
Cite this page:
Agency Echelon. "How do you calculate reach and frequency?" Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/questions/how-to-calculate-reach-and-frequency/