# Definition: Frequency

In online advertising, frequency refers to how often an ad appears to a single user in a specific time frame. It is usually measured and expressed as a per hours figure, even when discussing a day. For example, if an ad appeared to a single user six times in one day, it would be said to have appeared 6/24 times (or 6 per 24 hours).

Frequency is an important measure because the number of times a user sees an ad affects the likelihood of them clicking on it (or buying a product because of it). In traditional advertising, it is thought that someone needs to be exposed to an advertising message about five times to be effective – this is referred to as opportunities to see (or OTS).

## Technical Information

For online advertising, it depends on the ad unit, but generally speaking, the best performance comes from a 3/24 frequency cap. This means each user sees an ad no more than three times a day. If an ad is more invasive (such as a pop-under or overlay), then a 1/24 cap is preferable. Both of these caps are likely the most amount of times a user can tolerate seeing a single ad campaign. Once they are annoyed by it, the effectiveness of a campaign tails off quickly.

If a single user sees an ad too often, they will likely tune it out. More than that, it is a waste of the advertiser’s money to show the same ad repeatedly to a single user. There is only so much any single user can click (or purchase from) one ad after all!

## Frequency Formula

To work out the approximate frequency of an ad,  you can divide ad impressions by unique users. This will be a rough measure only, as users will have seen the add different amounts of times. However, if you have a frequency cap in place, it will be pretty accurate comparatively.

The frequency equation is:

Click to enlarge

Frequency = Impressions ÷ Users (per timeframe measured)

Example: Thirty impressions served to three unique users in 24 hours would be expressed as 10/24 (as each user saw ten impressions).

## Other names (synonyms)

Opportunities to see

## Not to be confused with

Frequency Cap, Recency

Glossary Index