DNA sequence length in numbers of base pairs.
1 kbp (kilo base pairs) = 1,000 bp (base pairs)
1 Mbp (mega base pairs) = 1,000,000 bp
1 Gbp (giga base pairs) = 1,000,000,000 bp
Alternatively, kb, Mb, and Gb is sometimes used, but kbp, Mbp, and Gbp is often preferred to avoid confusion with gigabyte (GB) of computer disk space.