Most companies do not measure Mean Time Between Failure (MTBF). Yet, it is one of the first and most basic measurements you can use to measure reliability. MTBF is the average time an asset will function before it fails. This document is a guide which will take you from just starting to expert.

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MTBF User’s Guide
Measuring Mean Time Between Failure
Do you want stop failure? MTBF is the most used metric for failure elimination worldwide. This guide
will walk you through what you need to know to effectively measure MTBF within your organization.
A DIVISION OF ALLIED RELIABILITY GROUP

3. MTBF User’s Guide
Measuring Mean Time Between Failure
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Copyright 2013
A division of Allied Reliability Group
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GPAllied
4200 Faber Place Drive
Charleston, SC 29405
Office (888) 335-8276
Most companies do not measure Mean Time Between Failure (MTBF). Yet, it is one of the first and most basic
measurements you can use to measure reliability. MTBF is the average amount of time that an asset,
component, part, etc. will function before it fails.
Understand Definitions
It is important to have definitions because in reality, the true meaning of terms is not always what typical
industry believes. What is important is that everyone within your organization has a common understanding of a
definition.
 Bad Actors = Equipment or assets that have typically long-standing reliability issues. Some companies
identify “bad actors” by the amount of maintenance dollars spent on the assets in terms of labor and
material. MTBF is a simple measurement to pinpoint these poor performing assets. Note that the most
systematic, technically-based method of determining if an asset is critical is to conduct an assessment
based on consequence of failure and risk of failure to the business.
 Total Equipment Failure = Total Equipment Failure occurs when an asset completely fails or breaks
down; it is not operating at all.
 Partial Failure = The inability of an asset to fulfill one or more of its functions (for example, it no longer
produces product that meets quality standards, but the production line continues to meet production
rate or capacity).
 MTBF = The average amount of time that an asset will function before it fails.
 Emergency Work Order = A formal document that is written anytime an asset has a problem and a
maintenance person is called to investigate or make a repair.
 Reliability = The ability of an item to perform a required function under stated conditions for a stated
period of time.

4. MTBF User’s Guide
Measuring Mean Time Between Failure
www.gpallied.com
Copyright 2013
A division of Allied Reliability Group
Page 2
GPAllied
4200 Faber Place Drive
Charleston, SC 29405
Office (888) 335-8276
The Process
Step 1: Ensure that all work is covered by a work order, no matter how minor, and that the asset information is
captured in your Computerized Maintenance Management System (CMMS) or Enterprise Asset Management
(EAM) system by asset number.
Step 2: Begin tracking MTBF, focusing on one production area or asset group.
o Calculate on a daily basis the MTBF.
− For plants just starting to measure MTBF:
MTBF =
Time
Number of emergency work orders
(for all failures: total, functional, and partial)
− For more mature maintenance organizations:
MTBF =
Time
Number of maintenance events
(all events: planned, unplanned, or otherwise)
o Trend the data you find in this production area or asset group daily on a line graph and post it for
everyone to see.
**Many people may not like to see this data or even believe it, but it provides knowledge of how the
equipment has been performing to date and increases the awareness of the need to find a solution to
improve reliability.
o Once you feel comfortable tracking and trending MTBF for this one production area or asset group,
begin stepping down to the next level in your asset group. This group is typically called the “child” in
your equipment hierarchy. What you have been measuring thus far is what I call the ‘father’ or ‘parent’
in the equipment hierarchy. You may define the hierarchy differently, but in general the message is
understood.
o More mature maintenance organizations will want to switch to tracking all maintenance events,
planned or unplanned. Tracking to this level makes it much easier to see the total impact of all
maintenance decisions, not just the ones that result in lost production. At some point, the organization
has to come to terms with the fact that down is down, whether you planned it or not. Even if you did
plan it, it was an impending failure that has to be counted for the calculation of reliability for a system
or machine.
Step 3: Continue the process throughout your organization’s production areas and component/maintainable
items.

5. MTBF User’s Guide
Measuring Mean Time Between Failure
www.gpallied.com
Copyright 2013
A division of Allied Reliability Group
Page 3
GPAllied
4200 Faber Place Drive
Charleston, SC 29405
Office (888) 335-8276
Example of Calculation
 Number of emergency work orders in the past 24 hours = 8:
o Total equipment failure = 3
o Functional equipment failure = 1
o Partial equipment failure = 4
NOTE: Do not worry about the exact definition of each type of failure. An emergency work order
needs to be written any time an asset has a problem and a maintenance person is called to the
asset to investigate or make a repair.
 Time: 24 hours
 Calculation:
MTBF =
24 hours
= 3 hours
8 emergency work orders
Trend this data on a line or bar graph and measure it by day or by week depending on the amount of failures
you see. It may take 3 months to begin to send a trend, or you may find high variation in your maintenance
process.
Actual MTBF for 900 Electric Motors

6. MTBF User’s Guide
Measuring Mean Time Between Failure
www.gpallied.com
Copyright 2013
A division of Allied Reliability Group
Page 4
GPAllied
4200 Faber Place Drive
Charleston, SC 29405
Office (888) 335-8276
NOTE: If you find that measuring MTBF by day is too difficult to interpret, move to measuring
MTBF by week. In this case, you would measure the number of failures that occurred during a
week and divide this number into the number of operating hours that the equipment was
scheduled to operate.
Summary
The process of measuring MTBF is important for a company to know the current status of reliability in all of its
assets. From here, it can be determined which assets are in need of improved reliability.
We hope you find this document both useful and helpful. If you have any questions, please email Ricky Smith,
rsmith@gpallied.com, or Andy Page, apage@gpallied.com.

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