From a standard daily schedule, from a.m. to p.m. is 12 hours.

Quick Scoop: How long is a.m. to p.m.?

  • A day has 24 hours, split into two 12‑hour blocks.
  • The a.m. period runs from midnight (12:00 a.m.) up to just before noon (11:59 a.m.).
  • The p.m. period runs from noon (12:00 p.m.) up to just before midnight (11:59 p.m.).

So if you’re asking “how long is it from the start of a.m. to the start of p.m.?” that’s midnight to noon, which is 12 hours.

If instead you meant a specific time, like 8 a.m. to 8 p.m., that span is also 12 hours , because you’re going from morning to the same clock time in the evening.

One simple way to remember it: a.m. = before midday, p.m. = past midday; each side of noon lasts 12 hours.

TL;DR: From the a.m. period to the p.m. period (midnight to noon, or 8 a.m. to 8 p.m., etc.) is 12 hours.

Information gathered from public forums or data available on the internet and portrayed here.