A work order number is the one field that lets a job be found later: quoted on a part, written on a certificate, referenced from a corrective work order, searched for in an audit. It sounds trivial and it is one of the things sites get wrong for years. This page says what the number is for, which formats stay useful as the history grows into the thousands, and the mistakes, restarting each year, encoding meaning, and letting two systems number the same job, that make numbers meaningless.
What the number is for
Unique identification of one job, for its whole life and afterwards. It is what the requester quotes when asking about progress, what the technician writes on the part bag, what the certificate references, what the corrective work order points back to, and what the auditor asks for. A number that is unique and never reused does that; anything else it carries is optional and usually a liability.
Formats that stay useful
A plain sequence: WO-000001 onwards, never reset. A CMMS assigns it; a paper system uses a numbered pad or the next row in the log. A short prefix by site is worth having when there are several sites and one system, so that a number quoted by phone identifies the site. That is the whole of a good format, and it will still be unambiguous when the count is in six figures.
The mistakes
Restarting the sequence each year, so that WO-0142 exists five times. Encoding the asset, the date or the type in the number, which means the number changes when the job is reassigned or is wrong when the type is corrected, and which the record already holds in fields. Letting the request system and the work order system number separately so that one job has two numbers. And handwriting numbers on a pad without a sequence, which is how duplicates are born. Each of these is fixed by the plain sequence and never reused.
Linking numbers
A corrective work order references the number of the inspection that found the fault. A contractor's work order references the certificate. A follow-up references the breakdown. Those links are what make the history readable: from any work order you can walk to the one that caused it and the one it caused. A CMMS holds the links as fields; on paper it is a line at the bottom of the sheet, and the maintenance work order template worksheet on this site has it.
Questions people ask about work order number
Should the work order number include the date?
No. The date is a field. A number that carries the date is wrong the day the job is rescheduled and is one more thing to type.
What number does a request get?
The same number as the work order it becomes, if the systems are one. If they are two, the work order carries the request's number as a reference and its own as the identifier.
Can numbers be reused after a job is cancelled?
No. A cancelled job keeps its number with a cancelled status, so that the gap is explained.