### Repeat length

Repeat length refers to the maximal number of dinucleotide repeats within a primer. For example, the primer TCG CG CG CGT has a repeat length of 4, because it contains 4 consecutive GC-dinucleotides. Similarly to the run length, primers with too many repeats can lead to mispriming:

Intended binding mode
Primer | 5-TCG CG CG CGT-3'
Template | 3'-AAAGC GC GC GCA -5'

Binding mode resulting from mispriming
Primer | 5'-TCG CG CG CGT-3'
Template | 3'-AAAGC GC GC GCA -5'

The first, intended binding mode has a perfectly complementary primer, but the second, unintended binding mode also has a considerable number of complementary positions due to the large number of repeats.