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MTTF Calculator

MTTF Calculator — Mean Time To Failure

Enter total operating hours and the number of units to get MTTF for a non-repairable component, instantly.

MTTF
480 hrs
Average service life per unit before failure
MTTF in days
20 days
Assuming 24-hour equivalent days

What is MTTF?

MTTF stands for Mean Time To Failure — the average time a non-repairable component operates before it fails and is replaced, not repaired. Bearings, seals, fuses, gaskets — components you swap out rather than fix.

This is the key distinction from MTBF: MTBF measures a repairable asset that returns to service after a breakdown. MTTF measures a component's expected service life before it's simply thrown away and replaced.

MTTF = Total operating hours ÷ Number of units, measured across a batch of identical components in service or under test.

Worked example

A plant runs 125 identical conveyor rollers. Tracked over a period, they accumulate 60,000 combined operating hours before each one has failed and been replaced.

MTTF = 60,000 hours ÷ 125 units = 480 hours

On average, each roller runs 480 hours before it needs replacing. That number is what drives spare-parts stocking — order the next batch before the fleet starts hitting that mark, not after.

MTTF vs. MTBF vs. MTTR

  • MTTF — expected service life of a non-repairable component before replacement. The metric on this page.
  • MTBF — how long a repairable asset runs between breakdowns. Use the MTBF calculator for that.
  • MTTR — how long it takes to fix a repairable asset once it has failed. Use the MTTR calculator for that.

The dividing line is repairability: if it gets fixed, it's MTBF/MTTR territory. If it gets thrown away and replaced, it's MTTF.

Why MTTF matters for spares strategy

MTTF is the number that should drive your spare-parts stocking decisions. Components with a low MTTF relative to how long you need the machine to run need to be kept in stock — running out mid-shift turns a planned swap into an unplanned breakdown, which shows up as MTTR on the repairable asset that component sits inside.

If you're tracking both, low MTTF components are exactly the ones worth cross-checking against your MTTR data — a spike in repair time often traces back to a stockout on a low-MTTF part.

Frequently asked questions

What does MTTF stand for?
MTTF stands for Mean Time To Failure. It is the average time a non-repairable component or unit operates before it fails and is replaced — not repaired. Bearings, seals, fuses, and light bulbs are typical examples.
What is the formula for MTTF?
MTTF = Total operating hours ÷ Number of units. Total operating hours is the combined runtime across every unit in the batch before it failed. This differs from MTBF, which divides by number of failures for a single repairable asset over time — for a batch of non-repairable units tested to failure, the two numbers converge, since every unit eventually fails exactly once.
What is the difference between MTTF and MTBF?
MTTF applies to non-repairable components — bearings, seals, fuses — that are replaced when they fail rather than repaired. It measures expected service life before replacement. MTBF applies to repairable assets — machines that return to service after a breakdown. In factory maintenance, MTBF is the metric for production equipment; MTTF matters for spare-part specification and stocking decisions.
What is a good MTTF value?
There is no universal benchmark — it depends entirely on the component type, its operating environment, and manufacturer specifications. What matters is comparing MTTF against your actual replacement interval: if components are failing well before their rated MTTF, something in the operating conditions or the batch quality needs investigating.

Tracking this metric by hand?

MachDatum CMMS calculates it automatically from your work-order history — no spreadsheets, no manual tally.

Book a Demo Read the MTBF guide

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