How to judge ssDNA size

[wliu at receptor.pharm.uwa.edu.au]

Hi, netters,
I run isolated ssDNA (size is 6.2 kbp) on gel along with 1kb. The band
is not in 6 kbp position but around 2-3 kb position. If I haven't used
the ssDNA maker, how can I roughly judge the ssDNS size from the ds
DNA maker(such as 1 kb) so that I know I got the right size ssDNA? If
anyone has idea about this, please emial me.
Many thanks.
Weihong