Composite SLA Calculator (Serial and Parallel)
Combine the availability of up to three components to see the overall result.
Your numbers
Your results
Composite SLA Calculator (Serial and Parallel) by TheCalcTools
How the Composite SLA Calculator (Serial and Parallel) works
Enter the availability of each component.
In series, every component must be up, so you multiply the availabilities.
In parallel, the system is down only if all components are down, so you multiply the unavailabilities.
The formula
Worked example
Using the default values shown in the calculator:
| Component 1 availability (%) | 99.95 |
|---|---|
| Component 2 availability (%) | 99.9 |
| Component 3 availability (%) | 99.99 |
- Series: 0.9995 × 0.999 × 0.9999 = 99.8401%.
- Parallel: 1 − (0.0005 × 0.001 × 0.0001) ≈ 100.0000%.
- Series downtime is about 14h 0m 37.1s per year.
Result:
| In series (all must work) | 99.8401 |
|---|---|
| In parallel (any one works) | 100.0000 |
| Series downtime per year | 14h 0m 37.1s |
| Parallel downtime per year | 0h 0m 0.0s |
Frequently asked questions
Why is a chain of services less reliable than each part?
Each dependency adds a way to fail. Three 99.9% services in series give about 99.7%.
Does redundancy always give the parallel result?
Only if failures are independent and failover works perfectly. Shared causes such as a common region or a bad deployment reduce the benefit.
Sources and further reading
Related calculators
More in Cloud & Networking · All calculators
This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.