Work out nines to downtime instantly with clear inputs, formula shown and shareable results.
Allowed downtime is (1 - availability) multiplied by the period. The familiar landmarks follow directly: three nines gives 8.76 hours a year, four nines 52.6 minutes, and five nines just 5.26 minutes. Each additional nine cuts the allowance tenfold, which is why the cost of reliability grows so steeply at the top end.
Downtime from availability
downtime = (1 - availability) x period; 99.9% = 43.2 min/month, 99.99% = 4.32 min/month
5.26 minutes a year leaves no room for a single manual intervention. Every failure must be handled automatically, which requires full redundancy at every layer including the ones you do not control.
Enormously. Four nines measured monthly allows 4.3 minutes each month; measured annually it allows 52 minutes, which could all fall in one bad day.