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Free functional safety calculators
The four calculations engineers look up most often, done properly: proof test coverage and mission time included, formulas on the page, results you can check by hand. Everything runs in your browser.
Calculators
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SIL verification
PFDavg calculator
1oo1, 1oo2, 2oo2, 2oo3 and 1oo3 with β, repair times, proof test coverage and mission time. IEC 61508-6 simplified value beside the time-domain average, and PFD(t) with dates.
Open the PFDavg calculator -
SIL determination
LOPA calculator
Initiating event, enabling conditions, conditional modifiers and protection layers, to the mitigated event frequency, the required risk reduction and the target SIL.
Open the LOPA calculator -
Testing
Proof test interval calculator
The longest interval that keeps a subsystem within its target, and when coverage makes the target unreachable. Test due dates included.
Open the interval calculator -
Failure data
Failure rate converter
FIT, per hour, per million hours, per year and MTTF; failures to expect across a fleet; the λDD / λDU split from diagnostic coverage and the safe failure fraction.
Open the converter
Where the free calculators stop
A safety function is more than one subsystem. These pages answer one question each; First Out AI answers the one a reviewer asks.
| Question | Free calculators | First Out AI |
|---|---|---|
| PFDavg of one subsystem | Yes, five votings | Any voting up to four channels, partial stroke testing |
| Whole function in series | No | Sensors, logic solver and final elements, with each one's share of the result |
| Fault tolerance and systematic capability | No | Route 1H, Route 2H, IEC 61511 minimum HFT, SC per element |
| High demand mode (PFH), spurious trips | No | Yes |
| LOPA | One scenario | Scenario register, risk matrix and risk graph calibration, target passed to verification |
| Documents | No | SRS and proof test procedure drafts, HAZOP and cause & effect, PDF and Excel |
| Explanation | Formulas on the page | Engineer's reading of every result and an AI assistant grounded in your inputs |
Built to be checked
Every free calculator uses the same equations as the First Out AI engine and is tested against it: hundreds of random cases per release, plus hand-checked examples printed on each page.
- Formulas on the pageEach calculator shows its equations, symbols and a worked check you can repeat on paper.
- Nothing leaves your browserThe free calculators run locally; no account, no tracking of what you enter.
- Your data, your sourceNo licensed failure database is bundled; you enter rates from the certificate or FMEDA.
- Engineering judgement stays yoursFree aids, not certified software. A competent engineer checks every result.
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