How much downtime does 99.9% availability allow?

99.9% (three nines) = 8.77 hours/year. 99.99% = 52.6 minutes/year. 99.999% = 5.26 minutes/year. 99.9999% = 31.5 seconds/year. Each additional nine reduces annual downtime by ~90%.

How is composite availability calculated?

For services in series: A_total = A_1 × A_2 × ... For parallel redundancy: A_total = 1 − (1−A_1)(1−A_2).... Two 99.9% services in series give 99.8%; in parallel give 99.9999%.

Availability % from MTBF/MTTF Calculator

Calculate system availability A = MTTF / (MTTF + MTTR) = MTTF / MTBF. Converts to percentage uptime and maps to SLA nines (99.9%, 99.99%, etc.) with equivalent annual downtime.

Networking

Algorithms

Binary & Number

Systems

Dev Metrics

IP Subnet Calculator

IP Address

CIDR Prefix

Network

192.168.1.0

Broadcast

192.168.1.255

Subnet Mask

255.255.255.0

First Host

192.168.1.1

Last Host

192.168.1.254

Usable Hosts

254

Binary breakdown:

IP: 11000000.10101000.00000001.00000000

Mask: 11111111.11111111.11111111.00000000

Net: 11000000.10101000.00000001.00000000

How to Use

Enter the values for the patient or scenario you are assessing. Calculate system availability A = MTTF / (MTTF + MTTR) = MTTF / MTBF. Converts to percentage uptime and maps to SLA nines (99.9%, 99.99%, etc.) with equivalent annual downtime. Use the availability from mtbf result to inform your clinical assessment.

Related Calculators

MTBF Calculator

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