Convert bp to kDa: estimate double-stranded DNA molecular weight from base pairs, kb or Mb at 0.66 kDa per base pair, or find DNA length from kDa.

Estimate double-stranded DNA mass using an average mass per base pair.

Optional settings
Blank uses 0.660 kDa/bp, the usual average for double-stranded DNA; 0.650 is also common. Not for ssDNA or RNA.

Related Calculators

Base Pair to kDa Formula

The following formula is used to calculate the molecular weight (kDa) for a given number of base pairs and conversion factor.

MW = BP × CF

Variables:

  • MW is the molecular weight in kilodaltons (kDa)
  • BP is the number of base pairs
  • CF is the conversion factor (kDa/base pair)

To calculate the molecular weight, multiply the number of base pairs by the conversion factor. The default 0.660 kDa/bp is a conventional dsDNA average, not an exact sequence-specific mass. The 0.650 example is an alternative assumption; use the factor appropriate to composition, termini and counterion convention. See NEB nucleic-acid reference data.

Base Pairs to Kilodaltons Conversion Table (dsDNA, 1 bp ≈ 0.660 kDa)
Base Pairs (bp) Molecular Weight (kDa)
10066.000
200132.000
300198.000
400264.000
500330.000
750495.000
1,000660.000
1,200792.000
1,500990.000
2,0001,320.000
2,5001,650.000
3,0001,980.000
3,5002,310.000
4,0002,640.000
5,0003,300.000
6,0003,960.000
8,0005,280.000
10,0006,600.000
15,0009,900.000
20,00013,200.000
*Assumes double-stranded DNA average mass: 1 base pair ≈ 660 Da (0.660 kDa). Formula: kDa = bp × 0.660.

What is a Base Pair?

A base pair is a unit consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA. The most common base pairs are adenine with thymine (A-T) and cytosine with guanine (C-G) in DNA, and adenine with uracil (A-U) in RNA. The number of base pairs is often used to express the size of a gene or an entire genome.

How to Calculate Molecular Weight from Base Pairs?

The following steps outline how to calculate the molecular weight from base pairs.

  1. First, determine the number of base pairs (BP).
  2. Next, determine the conversion factor (CF) in kDa per base pair.
  3. Finally, calculate the molecular weight using the formula MW = BP * CF.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Number of base pairs (BP) = 1000

Conversion factor (CF) = 0.65 kDa/base pair

Using this explicitly chosen example factor, molecular weight = 1,000 × 0.65 = 650 kDa. The default 0.660 factor instead gives 660 kDa.