SESK: Stuff Everyone Should Know · sesk.info/tech-three-nines-downtime
About how much downtime does 99.9% monthly availability allow?
Three nines allows about 43.2 minutes in a 30-day month.
- 43.2 minutes ✔
- 4.3 minutes
- 26 seconds
Why: The unavailable fraction is 0.1%, or 0.001. Multiplying 30 days by 0.001 gives 0.03 day, which is 43.2 minutes.
Huh, didn't know that: Four nines allows about 4.3 minutes a month, and five nines about 26 seconds.
Three nines checked the clock and found 43.2 missing minutes.
Like this card?
References
Answer: 43.2 minutes. The unavailable fraction is 0.1%, or 0.001. Multiplying 30 days by 0.001 gives 0.03 day, which is 43.2 minutes.
- Google Cloud Building Blocks of Reliability docs.cloud.google.com/architecture/infra-reliability-guide/building-blocks
3 nines: 99.9% 43.2 minutes in a 30-day month
Checked 2026-10-10.
Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.
More stuff everyone should know
That's stuff everyone should know.