A hymn metre (Am. meter) indicates the number of syllables for the lines in each stanza of a hymn. This provides a means of marrying the hymn's text with an appropriate hymn tune for singing.
In the English language poetic metres and hymn metres have different starting points but there is nevertheless much overlap. Take the opening lines of the hymn Amazing Grace:
Analyzing this, a poet would see a couplet with four iambic metrical feet in the first line and three in the second. A musician would more likely count eight syllables in the first line and six in the second.
Completing that verse:
the hymnist describes it as 8.6.8.6 (or 86.86).
Conventionally most hymns in this 86.86 pattern are iambic (weak-strong syllable pairs). By contrast most hymns in an 87.87 pattern are trochaic, with strong-weak syllable pairs:
In practice many hymns conform to one of a relatively small number of metres (syllable patterns), and within the most commonly used ones there is a general convention as to whether its stress pattern is iambic or trochaic (or perhaps dactylic). It is rare to find any significant metrical substitution in a well-written hymn; indeed, such variation usually indicates a poorly constructed text.
All metres can be represented numerically. In addition, some of those most frequently encountered are named:
Often a longer verse will, in effect, be two short verses joined together or doubled. So:
A large number of hymns, including many well known ones, use other metres, for example, "Abide With Me" (10.10.10.10) and "Come Down, O Love Divine" (6.6.11.D).
Hymns written in a particular meter may be sung to any tune in that same meter, as long as the poetic foot (such as iambic, trochaic) also conforms.
Most hymnals include a metrical index of the book's tunes.