SLI Calculator

Calculate a service level indicator from successful events over total events.

About SLI Calculator

An SLI (Service Level Indicator) is the measured proportion of 'good' events out of all valid events in a window — for example, requests served under a latency threshold, or responses that weren't a server error. Formula: SLI = good_events / total_events × 100. Comparing the SLI to your SLO (Service Level Objective) target tells you whether you're in compliance, and the gap between the two — expressed as error budget — tells you how much unreliability you can still afford before breaching the SLO.

Formulas

Service Level Indicator

SLI = (good_events / total_events) × 100

good_events: Count of events meeting success criteria
total_events: Total valid events in the measurement window

Error budget consumed

error_budget_consumed_% = bad_events / (total_events × (1 - SLO_target / 100)) × 100

bad_events: total_events - good_events
total_events: Total valid events
SLO_target: Service Level Objective target percentage

Worked example

With the default values below, SLI Calculator returns SLI (Service Level Indicator) of 99.8500%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Good Eventsaccepts 0–1,000,000,000,000 events: 998,500 events
Total Eventsaccepts 1–1,000,000,000,000 events: 1,000,000 events
Measurement Windowaccepts 1–365 days: 30 days
SLO Targetaccepts 0–100 %: 99.9 %

Results

SLI (Service Level Indicator): 99.8500%
Meets SLO Target: false
Error Budget Consumed: 150.0%
Bad Events: 1,500
Margin vs SLO (pp): -0.0500

Step by step

1SLI: good / total × 100= 99.8500%
2Bad events= 1,500
3Error budget (events allowed to fail)= 1000 events
4Error budget consumed= 150.0%

Assumptions and limits

The result is derived only from the 4 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

What's the difference between SLI, SLO and SLA?

The SLI is the raw measurement (e.g. 99.95% success rate). The SLO is your internal target for that SLI (e.g. 99.9%). The SLA is the externally communicated commitment, usually with contractual consequences, and is often set looser than the SLO to leave margin.

What counts as a 'good event'?

It depends on the SLI type: for availability, a good event is a non-error response; for latency, it's a request under your threshold; for correctness, it's a response with the expected result. Define it precisely so measurement is consistent.

How is error budget useful day-to-day?

Error budget converts an abstract percentage into a concrete number of allowed failures. Once it's exhausted, many SRE practices pause risky releases and prioritize reliability work until the budget resets in the next window.

Why measure over a rolling window instead of calendar month?

A rolling window (e.g. trailing 28 days) gives a consistent, continuously updated view of reliability without discontinuities at month boundaries, which is why most SRE tooling defaults to it.