System Uptime Calculator
Calculate system uptime duration and availability percentage from boot timestamp.
About System Uptime Calculator
`/proc/uptime` reports two numbers: total seconds since boot, and total seconds the system has spent idle. Availability tracking uses the same ratio concept but at a service level — dividing total uptime by the sum of uptime and downtime over an observation window gives the availability percentage that SLA tiers ('three nines', 'four nines', etc.) are built around. This calculator projects that ratio forward to an expected annual downtime budget for easy comparison against SLA commitments.
Formula
Availability percentage
availability% = uptime / (uptime + downtime) × 100
- U
- total uptime
- D
- total downtime
Worked example
With the default values below, System Uptime Calculator returns Availability % of 99.8611%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Total Uptime (hours)minimum 0
- 719
- Total Downtime (hours)minimum 0
- 1
Results
- Availability %
- 99.8611%
- Approx. SLA Tier
- 99% (two nines)
- Projected Downtime (minutes/year)
- 730.0
- Total Observed Period (hours)
- 720.0
Step by step
- 1Values used
- 2Availability percentage
- 3Availability %= 99.8611
- 4Approx. SLA Tier= 99% (two nines)
- 5Projected Downtime (minutes/year)= 730.0
- 6Total Observed Period (hours)= 720.0
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How do I read /proc/uptime directly?
`cat /proc/uptime` prints two space-separated values in seconds: total time since boot, and total time the system has been idle (which can exceed real time on multi-core systems since idle time is summed across cores in some kernel versions — always sanity-check against `uptime -p`).
What's a realistic availability target for a self-hosted server vs. cloud SLA?
Cloud providers commonly commit to 99.9%–99.99% for compute SLAs (roughly 8.7 hours to 52 minutes of allowed annual downtime). A single self-hosted Linux box with manual patching and no redundancy typically lands lower, often 99–99.5%, once planned maintenance and occasional unplanned reboots are counted.
Does uptime alone measure availability?
Not fully — a host can be 'up' (kernel running) while the service it hosts is unresponsive (hung process, exhausted connections, network partition). True service availability should be measured via application-level health checks, not just kernel uptime.