90 Minute Timer
A 90 minute timer counts down 5,400 seconds and sounds an alarm when it reaches zero. That is 1 hour 30 minutes, recorded as 1.5 hours on a timesheet.
A ninety minute timer matches one ultradian cycle, the roughly ninety minute rhythm the body runs through in both sleep and waking attention.
Paused at 1:30:00
What a 90 minute timer is used for
Deep work, sleep cycles, exams and film-length sessions.
- One ultradian cycle
- Nathaniel Kleitman's basic rest-activity cycle runs about ninety minutes, and alertness dips at the end of each one.
- One sleep cycle
- A full sleep cycle averages ninety minutes, which is why sleep is easiest to wake from in multiples of it.
- Deep work sessions
- Ninety minutes is the block length used by most deep work practitioners, capped there because the cycle ends whether or not the task does.
- Exams
- Ninety minutes is a standard paper length, and pacing it is a skill practised against a real countdown.
Structuring a ninety minute deep work session
Pick one demanding task and decide what finished looks like for this session. Clear the first ninety minutes of the day if you can, before meetings and messages start, and put your phone in another room. The first ten or fifteen minutes are often slow. That is warm-up, not failure.
When the timer ends, stop and take a proper break of twenty minutes or more away from the desk. Before you go, write down where you stopped and the next step, so the next session starts quickly instead of with ten minutes of rereading.
The 90 minute timer at a glance
| Attribute | Value |
|---|---|
| Length | 1 hour 30 minutes |
| Seconds | 5,400 |
| Decimal hours | 1.5 |
| Clock format | 1:30 |
| In hours | 1.5 hours |
| Blocks per 8 hour day | 5 |
| Pomodoros (25 min each) | 3.6 |
| Break that pairs with it | 20 minutes |
| Decimal hours are rounded to two places, as payroll does. Block counts are whole blocks with no breaks between them. | |
For other lengths, use the minutes to decimal hours converter or the hours calculator.
Your focus time, counted and kept
A countdown tells you when the block ends. PomoTodo records that the block happened, which task it went to and what the week added up to, so a month of 90 minute blocks becomes something you can actually look at.
Free plan tracks unlimited focus time across unlimited tasks. No card required.
Timers either side of 1 hour 30 minutes
If 1 hour 30 minutes is the wrong length, the two nearest are 1 hour and 2 hours.
For the method rather than the countdown, see a study timer with longer blocks.
Questions about the 90 minute timer
Why ninety minutes for deep work?
It matches the basic rest-activity cycle described by sleep researcher Nathaniel Kleitman, which runs through waking hours as well as sleep. Alertness rises and then falls across roughly ninety minutes, so ending a block there means stopping at a natural trough rather than fighting through one.
How many ninety minute sessions can I do in a day?
Many people find two or three is their limit for genuinely demanding work. Beyond that, quality tends to drop, and the time is better spent on meetings, admin and lighter tasks.
How long a break should follow ninety minutes of work?
Twenty to thirty minutes, and it should involve leaving the desk. The break after a full cycle is doing more work than a five minute Pomodoro break, because it has a genuine dip in alertness to recover from.