We like to use Bioline's HyperLadder molecular weight standards; they have bands at metric sizes and DNA concentrations. With this you can easily estimate DNA concentration by eye. --Jered HyperLadder I has bands at: 10,000 bp 100 ng/band 8,000 80 6,000 60 5,000 50 4,000 40 3,000 30 2,500 25 2,000 20 1,500 15 1000 100 800 80 600 60 400 40 200 20