The formula
Cost per 3-second play = spend / 3-second video playsA Kestrel & Vane 20-second video gets 60,000 impressions, 18,600 three-second plays and $540 in spend. That is a 31.0% hook rate and $540 / 18,600 = $0.029 per 3-second play. A static ad in the same ad set shows no 3-second plays at all, because there is no video to play.
Why it matters
Three seconds is roughly where a scroll turns into a choice. The raw count says little on its own, since it grows with spend, but it is the base for the ratios that do: hook rate (how many stopped) and hold rate (how many stayed). Watch for inflated counts: other play columns that log any start of a video, including autoplay starts that last a fraction of a second, make a hook look far stronger than it is.
How to improve it
You earn more 3-second plays per impression by fixing the first frame: movement, a face, a clear product shot, or bold text that names the problem. Add captions so the opening makes sense with the sound off, since most feed video starts muted.