Calculadora de Número de Cópias de DNA
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
cópias = (ng × 6,022×10²³) / (pb × 660 × 10⁹)
About this calculator
The DNA Copy Number Calculator estimates how many DNA molecules are present in a sample based on mass, fragment size, and Avogadro's number. It is essential in molecular biology, especially in PCR, cloning, and sequencing experiments, where precise DNA quantification is critical. The calculator uses Avogadro's constant (6.022 × 10²³) and the average molecular weight of a base pair (660 Da) to convert mass (in nanograms) into copy number.
The calculation follows a straightforward formula: copy number = (mass in ng × 6.022 × 10²³) / (size in bp × 660 × 10⁹). The factor 10⁹ adjusts mass from nanograms to grams, since 1 ng = 10⁻⁹ g. For example, 1 ng of a 1000 bp fragment yields approximately 9.1 × 10⁸ copies. This conversion is fundamental for preparing dilutions, calculating templates for reactions, and normalizing samples.
Use this calculator when planning experiments that require an exact number of DNA molecules, such as in qPCR for absolute quantification, sequencing library preparation, or determining viral loads. It is also useful for verifying DNA extraction efficiency by comparing expected copy numbers with obtained ones. Note that the formula assumes linear double-stranded DNA; for circular or single-stranded DNA, adjustments may be needed.
Important precautions: accuracy depends on precise mass measurement (use a calibrated fluorometer or spectrophotometer) and fragment size (confirm by electrophoresis or sequencing). Contaminants like RNA or proteins can overestimate mass. Additionally, the formula assumes intact DNA; degraded fragments can lead to overestimation of copy number. Always validate results with positive controls.
Frequently asked questions
What is Avogadro's number and why is it used?
Avogadro's number (6.022 × 10²³) is the number of elementary entities (atoms, molecules) in one mole. It is used to convert DNA mass into number of molecules by relating molar mass to amount of substance.
Does the formula work for single-stranded or circular DNA?
The standard formula is for linear double-stranded DNA. For single-stranded, use 330 Da per base (half). For circular DNA, the molecule is continuous but calculation is similar; supercoiling does not affect mass.
How to accurately measure DNA mass?
Use a fluorometer with specific dyes (e.g., PicoGreen) or a spectrophotometer (absorbance at 260 nm). Avoid non-specific methods that may include contaminants.
What if the result seems too high or low?
Check units: mass in ng, size in bp. Confirm sample purity and integrity. Compare with known controls. If degraded, copy number may be overestimated.
Can I use this calculator for RNA?
Not directly. RNA has different molecular weight (about 340 Da per base) and is usually single-stranded. An adapted formula would be needed; this calculator is specific to DNA.