Understanding SAIDI
How we calculate. SAIDI (minutes) = Σ interruption customer-minutes ÷ customers served. See our methodology and accuracy policy .
Real-world scenario: A typical SAIDI case uses customer-minutes interrupted 2400000 and customers served 100000. Enter the same figures below to reproduce the worked path.
What is SAIDI?
A distribution reliability KPI. Distinct from forced outage rate (generating-unit forced hours÷period) and availability factor.
- Same reporting period
- Customers served = average or end-of-period per policy
- Major event days may be excluded in filings—label your basis
The Formula
Worked Example
Common Use Cases
- Utility reliability reports: SAIDI tracking
- Board scorecards: interruption duration
- Benchmarking: peer SAIDI comparisons
Pro Tips
- State minutes vs hours
- Align IEEE 1366 / regulator exclusions
- Don’t mix generation FOR into SAIDI
| Scenario | When to use |
|---|---|
| Percent of a number | Finding a part of a whole (tax, tip, score) |
| Percent change | Comparing old vs new values |
Limitations: SAIDI results are educational energy and utilities planning aids—not engineering, grid-operations, or investment advice. Confirm definitions with your ISO/RTO, plant, and regulatory reporting standards.
Common mistakes
- Swapping part and whole: The denominator must be the full total, not a subset.
- Rounding too early: Carry extra decimal places through multi-step work before rounding the final percent.
- Mixing percent and decimal forms: Enter rates in the format the calculator labels expect.
The worked example for saidi was verified with the calculator form on this page—enter the same values to confirm the result.
When to use this calculator
- Use this page when your wording matches saidi and the form labels on screen.
- Use percent of a number for “what is X% of Y?” problems.
- Use number is what percent when you know part and whole and need the percent.
Still unsure about saidi? Start with the quick answer above, then open the linked calculator that matches your wording.
❓ Frequently Asked Questions
How do I use this saidi calculator?
For saidi, enter the values labeled on the form, then press Calculate. Compare the result to the worked example on this page.
What formula does this page use?
See the quick answer and formula box above for saidi—the same percentage calculator expression is applied to your inputs.
What if my result looks wrong?
When checking saidi, re-check part vs whole (or rate vs base), rounding, and whether percents were entered as 25 rather than 0.25 when the form expects percents.
Authoritative References
For power system and plant performance concepts, consult: