The minimum audience size on every major ad platform
Four platforms publish a hard floor. Below it, campaigns are accepted, go live, and deliver nothing. Here's each one with its source.
Several platforms enforce a minimum below which an ad set simply won't run. None of them raise an error at setup. The campaign is created, the status looks healthy, and there's no delivery.
What each platform publishes
| Platform | Floor | Applies to |
|---|---|---|
| 300 member accounts | Per ad set. Split a test two ways and you need 600 in total. | |
| TikTok | 1,000 matched users | Custom audiences. Below this the audience can't be used at all. |
| Meta | 100 people from one country | Lookalike source audiences. |
| X | No minimum spend stated | X states there's no minimum campaign spend, so small tests are genuinely possible. |
The arithmetic people skip
A floor that applies per ad set multiplies by the number of cells in your test. This is the single most common way a well-designed experiment produces nothing: the audience was fine, the split wasn't.
Work it out before you write creative, not after. On LinkedIn especially, the forecast panel is the step that most often sends you back to the start.
What isn't on this list
Google, Pinterest, Reddit and YouTube either don't publish a comparable floor or didn't state one on the pages we read. Absence here means we couldn't verify one, not that none exists. Each spec page lists what we could and couldn't check.