Look up the running time of a well-known film in four places and you may get four answers, several minutes apart. The usual assumption is that someone made a mistake. Usually nobody did.
Films exist in versions
A single title routinely exists as a festival cut, a theatrical cut, a version trimmed for a classification board in a particular territory, a television edit with content removed and act breaks added, an airline edit, and one or more later cuts prepared for home video or restoration. Each is a real version with a real running time, and each has been the version someone measured.
Television edits diverge furthest. Material is cut for content and for time, and occasionally material is added — unused footage reinstated to fill a longer slot. A television version can be both shorter and longer than the theatrical one in different places.
The frame rate problem
Film is normally shot and projected at 24 frames per second. The older European television standard ran at 25. Converting film to that standard by showing each frame once speeds the film up by about four per cent, which shortens a two-hour film by roughly five minutes and raises the pitch of the soundtrack audibly.
This affects a great deal of material mastered for European television and early home video. A runtime taken from such a master is genuinely different from the same film measured at its native rate, and neither figure is wrong.
What counts as the film
Sources also differ on what they are measuring. Some figures include the distributor's logos and the full end credits; some stop at the last frame of picture; some are taken from the certificate issued by a classification board, which measures the print submitted to it and may predate final changes.
Aspect ratio and framing
The same disagreement affects the image. A widescreen film shown full-frame on older television was either cropped at the sides or panned and scanned — reframed shot by shot to follow the action. Some films were shot with this in mind and protected extra image above and below the widescreen frame, so the full-frame version can show more picture vertically while showing less horizontally.
A restoration then makes a judgement about the intended framing, which may differ from how the film was actually exhibited at the time. The intended and the historical framing are both defensible and are sometimes not the same.
Citing a runtime usefully
A running time on its own carries less information than it appears to. A running time attached to a version and a source — theatrical cut, 24 fps, as classified in a named territory — is a fact someone else can check. Where a database gives a single number with no version attached, it is best read as an approximation of the most widely circulated version, which is a useful thing to know and a poor thing to quote precisely.