If you know something about this primer, you must also check that it is a ISSR and polymorphic marker. It is not having a single band. Thus no one can give answer to your question. This primer produces multiple bands depends on what template you are using.

following

The publication reported these primers should provide you with the size of the PCR prodict based on the sequence and purpose of designation. Otherwise using these primers with related known DNA samples

and PCR products can be compared with known standard DNA marker to know the size.

As per publication (if specified). Otherwise from ncbi database check it.

Dear Shimekit Tadele,

I imagine the primer full name is UBC-812 and has the sequence repeat motif (5′–3′) (GA)8A if so look at the link of the paper in which the primer is mentioned:

Article Informative ISSR Markers Help Identify Genetically Distinct ...

You'll see that it is used in ISSR-PCR. In each PCR reaction a single primer is employed and the annealing temp reccommended for the primer UBC-812 is 47 (°C) . Check other details in the paper in which you will see also the photos opf the gels with the multiple bands after PCRs...

Best of luck

Stefania M. Mang