MTBF Calculator — Mean Time Between Failures

A hydraulic press runs two shifts (16 hours/day) over a 30-day month — about 480 operating hours available. It was down for unplanned repairs for 20 hours during that period, so actual operating time is 460 hours. The press broke down 4 times.

MTBF = 460 hours ÷ 4 failures = 115 hours

On average, this press runs for 115 hours before its next unplanned stop. Only unplanned breakdowns count as failures — scheduled PM stops and changeovers are excluded from the count, and downtime (not calendar time) is subtracted from the denominator.

These three metrics get confused constantly because they measure adjacent things on the same breakdown-and-repair cycle:

• MTBF — how long a repairable asset runs between breakdowns. The metric on this page.
• MTTF — expected service life of a non-repairable component (a bearing, a seal, a fuse) before it is simply replaced, not repaired. Use the MTTF calculator for that.
• MTTR — how long it takes to fix a machine once it has failed. MTBF tells you how often a machine stops; MTTR tells you how long it stays down each time. Use the MTTR calculator to get that number.

MTBF and MTTR together determine Availability — the share of planned production time a machine actually ran. A machine that breaks down less often (higher MTBF) and recovers faster (lower MTTR) has higher availability. Availability, in turn, is one of the three factors in OEE (Overall Equipment Effectiveness), alongside Performance and Quality.

If you're tracking OEE and want to see where the loss is coming from, start with MTBF and MTTR per asset — they're the inputs to the Availability component, which is usually where the biggest OEE losses sit. Run the numbers through the Availability calculator or the OEE calculator next.