TimerStopwatch.com

12 Hour Timer

This free 12 hour timer counts down 12 hours (43,200 seconds) and rings an alarm at zero. It is already set — press Start or the space bar and it begins. It keeps time in a background tab, and full screen makes the digits big enough to read across a room.

12:00:00
Ready

Set the time

Shortcuts Space start / pause R reset F full screen + add a minute Esc stop alarm

12 hours at a glance

Duration12 hours
On the clock12:00:00 (h:mm:ss)
In seconds43,200
In minutes720
In hours12
Share of a day50%
Start now, ends at—

What is a 12 hour timer good for?

Twelve hours is half a day: a long shift, an overnight marinade or dough, or the gap between two doses of something you take twice a day.

  • Long work shifts
  • Overnight marinades and doughs
  • Twice-daily reminders
  • Fasting windows

← 8 Hour Timer 24 Hour Timer →

How to use the 12 hour timer

  1. Press Start

    The timer is already set to 12 hours. Press Start or Space.

  2. Watch the ring

    The ring empties as time passes, and the tab title counts down with it so you can check from another tab.

  3. Adjust if you need to

    Pause any time, press +1 min to add a minute, or change the time in the panel.

  4. Stop the alarm

    At zero the alarm rings. Press Stop alarm or Esc, or +1 min to snooze.

Other quick timers

One click starts the countdown — every preset rings an alarm, works full screen and keeps time in a background tab.

Seconds

Minutes

Hours

Frequently asked questions

How do I start a 12 hour timer?

Press Start (or the space bar) on this page — the timer is already set to 12 hours. When it reaches zero the alarm rings until you stop it or the ring time you chose runs out.

How many seconds are in 12 hours?

12 hours is 720 minutes, or 43,200 seconds.

Will the 12 hour timer ring if I switch tabs?

Yes. The alarm is scheduled ahead on your browser’s audio clock, so background-tab throttling cannot delay it. Turn on notifications in the panel to get a pop-up too. If you reload the page, it keeps counting from where it was.

Can I pause the timer or add more time?

Yes. Pause stops the countdown and Start resumes it. +1 min (or the + key) adds a minute, and after the alarm it starts a one-minute snooze. To set a different length, use the time boxes, the number pad, or one of the other quick timers.

More free timing tools

Online Stopwatch Lap and split times to 1/100 s, best and worst laps, CSV export. Pomodoro Timer 25-minute focus sessions and breaks, with auto-start and a daily tally. Interval Timer HIIT, Tabata, EMOM and boxing rounds with 3-2-1 beeps and voice cues. Countdown to a Date Days, hours, minutes and seconds to any date and time zone, shareable by link. Tabata Timer20 seconds on, 10 seconds off, eight rounds — four minutes, done.

Last reviewed October 31, 2026