# FIT Failure Rate to MTBF Conversion Calculator

> Source: https://netray.co/tools/fit-failure-rate-mtbf-conversion-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Convert a FIT rate to MTBF, expected failures per year across a fleet and the reliability over a mission.

## Category

electronics

## Industry

Electronics

## Audience

- Reliability engineer
- Electronics engineer
- Field quality

## Tool

**Kind:** calculator

**Inputs:**

#### Failure rate

**Key:** fit

**Type:** number

**Default:** 250

**Min:** 0

**Step:** 10

**Unit:** FIT

**Help:** Failures per 10^9 device hours, for example from a reliability prediction or qualification data.

#### Devices in the field

**Key:** devices

**Type:** number

**Default:** 20000

**Min:** 0

**Step:** 500

**Unit:** units

#### Powered hours per year

**Key:** duty

**Type:** number

**Default:** 8760

**Min:** 0

**Max:** 8760

**Step:** 100

**Unit:** hours

**Help:** 8760 means continuously powered.

#### Mission time

**Key:** mission

**Type:** number

**Default:** 50000

**Min:** 0

**Step:** 1000

**Unit:** hours

**Outputs:**

#### Failure rate per hour

**Key:** lambda

**Expr:** fit / 1000000000

**Format:** decimal

#### MTBF

**Key:** mtbf

**Expr:** if(gt(fit,0), 1000000000 / fit, 0)

**Format:** number

**Primary:** true

**Description:** Hours, assuming a constant failure rate.

#### MTBF in years of continuous operation

**Key:** mtbf_years

**Expr:** mtbf / 8760

**Format:** years

#### Expected fleet failures per year

**Key:** fails_year

**Expr:** fit * devices * duty / 1000000000

**Format:** decimal

**Primary:** true

#### Reliability over mission time

**Key:** rel

**Expr:** exp(0 - fit * mission / 1000000000) * 100

**Format:** percent

**Chart:**

#### Reliability (%) vs mission time

**Type:** line

**X:** mission

**From:** 1000

**To:** 200000

**Steps:** 40

**Series:**

- rel

**Disclaimer:** Assumes a constant failure rate (useful life region). It does not model infant mortality or wear-out.

## Content

**Intro:** FIT is the unit of failure rate used in semiconductor and electronics reliability. This calculator turns it into MTBF and into a forecast of field failures.

**Sections:**

#### How to use the calculator

**Body:** Enter the failure rate in FIT, the number of devices in service and the powered hours per year. Add a mission time to see reliability over that period. The calculator reports MTBF, expected fleet failures per year and the reliability. Use it to size spares, set warranty reserves or sanity check a supplier's claim.

#### The formulas

**Body:** One FIT equals one failure per billion device hours. MTBF in hours equals 10^9 divided by FIT. Expected failures equal FIT times devices times hours divided by 10^9. Reliability over time t is exp(-lambda t) where lambda is FIT divided by 10^9. A 250 FIT part has an MTBF of four million hours, about 457 years, yet a fleet of 20,000 can still see a handful of failures each year.

**Bullets:**

- MTBF is not the expected life of one unit.
- Add FIT values of series components to get a board or system rate.

#### Reading the result

**Body:** A very large MTBF only means a low constant rate; it says nothing about wear-out. Use the fleet failure count to judge service and spares load. If the count seems high, look at the parts contributing the most FIT and consider derating or redundancy as part of the DFMEA response.

#### Common mistakes

**Body:** Confusing MTBF with life is the most frequent error. Another is mixing failure rates at different temperatures or stress levels; predictions such as those based on handbook methods are tied to stated conditions. Check that the duty hours reflect real use and that returns are not counted as failures when no fault is found.

**Cta:** Netray can help match installed base and field returns from your ERP and service records against predicted failure rates.

**Faq:**

#### What does FIT stand for?

**Answer:** Failures In Time. One FIT is one failure per one billion device hours, equivalent to a failure rate of 1e-9 per hour.

#### Is MTBF the same as life?

**Answer:** No. With a constant failure rate about 63 percent of units fail by the time equal to MTBF. It describes rate during useful life, not time to wear out.

#### How do I add parts together?

**Answer:** For a series system, add the FIT values of all parts, then convert the total to MTBF. Redundancy needs a block diagram approach.

#### Why does the chart show a smooth curve?

**Answer:** Reliability decays exponentially with mission time at a constant failure rate, falling faster as mission time approaches the MTBF.

## Search terms

fit to mtbf calculator, failures in time calculator, mtbf from failure rate, fit rate conversion, expected field failures calculator, electronic component failure rate, mtbf to fit, fleet failure forecast

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