SLA Availability Calculator

Convert MTBF and MTTR into availability, the nines it earns and the downtime allowed per year, month and week.

Inputs

Mean time between failureshours

Mean time to repairhours

Independent redundant pathspaths

Availability

99.95436%

Nines Achieved

Three nines (99.9%) — 8.77 h/year

Downtime per Year

4.00hours

Downtime per Month

20.0minutes

Downtime per Week

4.6minutes

Step by step

Values used
Mean time between failures = 8,760 hours; Mean time to repair = 4 hours; Independent redundant paths = 1 paths
SLA Availability
availability = MTBF ÷ (MTBF + MTTR); for N independent parallel paths, unavailability is raised to the power N.
Downtime budget
Downtime per year = (1 − availability) × 8760 hours, so 99.9% allows 8.77 hours.
Availability
= 99.95436
Nines Achieved
= Three nines (99.9%) — 8.77 h/year
Downtime per Year
= 4.00 hours
Downtime per Month
= 20.0 minutes
Downtime per Week
= 4.6 minutes

How it works

Availability is the share of time the system is up, which is repair-time-weighted rather than failure-count-weighted. Truly independent redundant paths multiply the unavailabilities, which is why two 99.9% paths approach 99.9999% — provided they share no fibre, power feed or software version. SLA credits are written in nines but paid in minutes, and the per-month figure is the one an operations team can actually manage against.

Formulas

SLA Availability

availability = MTBF ÷ (MTBF + MTTR); for N independent parallel paths, unavailability is raised to the power N.

MTBF: Mean time between failures
MTTR: Mean time to repair
N: Number of independent redundant paths

Downtime budget

Downtime per year = (1 − availability) × 8760 hours, so 99.9% allows 8.77 hours.

Frequently Asked Questions

How is SLA Availability calculated?

availability = MTBF ÷ (MTBF + MTTR); for N independent parallel paths, unavailability is raised to the power N. Availability is the share of time the system is up, which is repair-time-weighted rather than failure-count-weighted. Truly independent redundant paths multiply the unavailabilities, which is why two 99.9% paths approach 99.9999% — provided they share no fibre, power feed or software version.

Why does SLA Availability matter?

SLA credits are written in nines but paid in minutes, and the per-month figure is the one an operations team can actually manage against.

What values do I need to enter?

This calculator takes 3 inputs: Mean time between failures, Mean time to repair, Independent redundant paths. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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