Reliability · SRE
Multi-window burn rate alert calculator.
Choose the share of error budget you are willing to lose before alerting and get the burn-rate and error-rate thresholds for any SLO and window.
Inputs
Result
Enter the values above.
How multi-window, multi-burn-rate alerts work
The Google SRE Workbook recommends alerting when the error budget burns quickly over a long window and is still burning over a short one. Budget consumed when an alert fires = burn rate x alert window / period, so burn rate = budget consumed x period / window. For a 30-day (720-hour) period, spending 2% in one hour is 0.02 x 720 / 1 = 14.4; 5% in six hours is 6; 10% in three days (72 hours) is 1. These are the workbook's Table 5-8 values for a 99.9% SLO: page at 14.4 (1 hour, 5 minute check), page at 6 (6 hours, 30 minute check), ticket at 1 (3 days, 6 hour check).
The error-rate threshold is burn rate x (100% - SLO). The short window defaults to one twelfth of the long window, as in the workbook pairs (1 h and 5 min; 6 h and 30 min). The percentages are the workbook's example choices, not requirements. Note that a very tight SLO plus a high burn rate can need an error rate above 100%, which can never fire.
Frequently asked questions
What is a good burn rate alert threshold?
The Google SRE Workbook example pages at 14.4 for 1 hour, 6 for 6 hours and opens a ticket at 1 for 3 days, on a 99.9% SLO over 30 days.
Why use two windows?
The long window avoids paging on brief spikes; the short window makes the alert reset quickly once the problem stops.
How is 14.4 calculated?
2% of the budget in 1 hour of a 720-hour month: 0.02 x 720 / 1 = 14.4.
Do these thresholds change with the SLO?
The burn-rate values do not, but the error rate that triggers them does: it is burn rate times the allowed error rate.
Sources
Checked
Formulas follow the sources above. Periods use a 30-day month and a 365-day year. Runs entirely in your browser; nothing you type is sent or stored.
Scope
Planning estimates only. Your SLA contract defines its own measurement window, exclusions and remedies, and those override these generic figures. Theoretical availability assumes independent failures.