Uptime Percentage Calculator
Turn measured downtime into an uptime percentage for the period.
In short
Formula: Uptime = (Measured time − Downtime) / Measured time, where Measured time = Period − Excluded time
What this calculator does
Time-based availability as described in the SRE workbook. Any exclusion is the user's own and is removed from the denominator as well as the numerator, so an excluded window neither helps nor harms the figure.
Use it to turn Length of the period measured, Unavailable time in the period, Time excluded by agreement (optional) into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this professional & industry calculation.
Inputs and what they mean
- Length of the period measured
- — Total time in the window you are reporting on..
- Unavailable time in the period
- — Minutes the service was unavailable, as you measured it..
- Time excluded by agreement (optional)
- — Optional component. Leave at 0 to exclude it from the result. Only minutes your agreement actually excludes, such as an agreed maintenance window..
How to use it
- Enter your own figures — the calculator never fills in a rate, price or benchmark for you.
- Press Calculate to see the result.
- Read the formula, variables, assumptions and source below the result before you rely on it.
Formula
Uptime = (Measured time − Downtime) / Measured time, where Measured time = Period − Excluded time.
Inputs used: Length of the period measured, Unavailable time in the period, Time excluded by agreement (optional).
Edge handling: Length of the period measured is required.; Length of the period measured cannot be negative.; Length of the period measured must be no more than 1000000000000.; Unavailable time in the period is required.; Unavailable time in the period cannot be negative..
Worked example
43 minutes down in a 30-day month
- Start with Length of the period measured: 720, Unavailable time in the period: 43, Time excluded by agreement (optional): 0.
- Apply the method: Uptime = (Measured time − Downtime) / Measured time, where Measured time = Period − Excluded time.
- Measured uptime only. Whether it meets a target is a separate question.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this uptime percentage calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: Google — Implementing SLOs
Last reviewed:
Common questions
Where does this formula come from?
Implementing SLOs — a service level objective is the share of good events among valid events (or of available time in the period); the error budget is the remainder that the objective permits. See the source link on this page.
What kind of calculation is this?
Available time as a share of the time actually being measured. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
What are its limits?
Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete. A mean over a short period, or over few events, is a weak description of behaviour. A time-based figure can hide partial failures that a request-based objective would count.
How do I use the Uptime Percentage Calculator?
Enter the required values for Length of the period measured, Unavailable time in the period, Time excluded by agreement (optional). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Uptime Percentage Calculator use?
Uptime = (Measured time − Downtime) / Measured time, where Measured time = Period − Excluded time The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
Can the Uptime Percentage Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Formula, source and verification
Available time as a share of the time actually being measured.
The question it answers: What availability, uptime, mean time between failures and mean time to repair does our own data show?
The formula
Uptime = (Measured time − Downtime) / Measured time, where Measured time = Period − Excluded time
- P — Period
- (h). Length of the reporting window.
- D — Downtime
- (min). Unavailable minutes as the user measured them.
- E — Excluded time
- (min). Only time the user's agreement actually excludes.
Units: Hours for the period, minutes for downtime, percentage out.
What kind of calculation this is
Deterministic formula. The same inputs always give the same answer. The maths is fixed and does not depend on judgement.
Method
Time-based availability as described in the SRE workbook. Any exclusion is the user's own and is removed from the denominator as well as the numerator, so an excluded window neither helps nor harms the figure.
Assumptions built into the result
- Mathematical: The figures entered all cover the same measurement period.
- Mathematical: Incidents, changes and requests are counted consistently with the definition the team has written down.
- Mathematical: Downtime is measured by the same monitoring the report is based on.
Figures this calculator will never guess for you
- No target, benchmark, industry average or performance band is supplied for any figure.
- A definition is never presented as a goal: the availability formula is not an availability target, and the change failure rate formula is not an acceptable failure rate.
- No maintenance window is excluded unless the user enters it.
Limitations
- Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete.
- A mean over a short period, or over few events, is a weak description of behaviour.
- A time-based figure can hide partial failures that a request-based objective would count.
Source and version
- Standard or reference
- Google SRE Workbook — Implementing SLOs — Google SRE (Implementing SLOs — a service level objective is the share of good events among valid events (or of available time in the period); the error budget is the remainder that the objective permits.)
- Published source
- Google — SRE Workbook
- Formula version
- Version 1
- Verification
- Reviewed against the cited source on
- How much weight the source carries
- Standards or government
- Applies to
- Currency
- The result is a ratio or index, so it does not depend on currency.
Related tools
Work out the hourly rate to charge a client so that target margin is met after overhead and non-billable time.
Find the true hourly cost of an employee once benefits, payroll cost and overhead are included.
Size a software application from its data and transaction functions before estimating effort or cost.
Estimate development effort, schedule and average team size for a software project of a known size.
Express cloud spend as a cost per customer, per transaction or per other business unit.
Set the rate used to apply manufacturing overhead to jobs for the coming period.