An amount of substance containing 6.02 * 10²³ copy particles is called a mole. The molar mass of a substance is equal to its relative formula mass in grams.

For Example:

Molecular weight of double stranded DNA sequence "TTAACCGGTTAA" is 7449.63 (Dalton).
One mole of which is 7449.63g.

1ng contains:
1 * 10^-9 * 6.02 * 10²³/7449.63 = 80809382479(copies).

If you don't have the sequence on hand, you can only input the sequence length, the calculation will based on the assumption that each base was 325 dalton. This will lose some accuracy.

Note: This calculation maybe useful:

→ When you extract DNA or RNA, the sequence was known, and you already measured the concentration, then you can get the copy number of the DNA or RNA by this calculation. Knowning the DNA copy number is important for designing experiment like Quantitative PCR.

→ When you synthesize primer, e.g. 25nmol, you can get the primer's copy number by this calculation. First paste the primer sequence in the text box, then input 25 in "Nanomole" input box, the result will shown.