DNA Concentration Calculator

Calculate nucleic acid concentration and total mass from A260 absorbance, dilution, and volume.

Calculate nucleic acid concentration

Choose the nucleic acid type and enter the spectrophotometer reading and sample details.

Nucleic acid type

Absorbance at 260 nm (A260)

Dilution factor

Sample volume (µL)

About DNA concentration measurement

Nucleic acids absorb ultraviolet light strongly near 260 nanometers because of their aromatic bases. A spectrophotometer measures that absorbance and the Beer-Lambert relationship connects it with concentration. This calculator applies the conventional laboratory conversion factors used for double-stranded DNA, single-stranded DNA, and RNA. It then multiplies by any dilution factor and by sample volume to report both concentration and total recovered mass. An A260 value of 1.0 is conventionally treated as 50 micrograms per milliliter for double-stranded DNA, 33 micrograms per milliliter for single-stranded DNA, or 40 micrograms per milliliter for RNA. Micrograms per milliliter is numerically equal to nanograms per microliter, so no additional scale conversion is needed for the displayed concentration. For a diluted reading, multiply by the dilution factor. A double-stranded DNA sample with A260 of 0.5 after a tenfold dilution is therefore 250 nanograms per microliter in the original sample. Accurate results depend on a properly blanked instrument, a clean optical surface, and a reading within the instrument's linear range. Blank with the same buffer used for the sample because salts, pH, and other components can affect the baseline. Mix the sample gently and avoid bubbles. If absorbance is too high, dilute the sample, measure again, and enter the complete dilution factor. The factor should describe original concentration divided by measured concentration; an undiluted sample has a factor of one. A260 alone does not prove that a sample is pure. Protein, phenol, guanidinium, free nucleotides, and turbidity can contribute to ultraviolet readings. Laboratories often examine A260 to A280 and A260 to A230 ratios as broad purity indicators. Fluorescent dye assays can provide better specificity when DNA concentration is low or when contaminants are likely. The chosen conversion factor is also an approximation, and unusual oligonucleotide sequences may require sequence-specific extinction coefficients. Use the total-mass result for recovery calculations, normalization planning, or deciding how much material is available for downstream work. It is simply concentration multiplied by sample volume, so it assumes the sample is homogeneous. Before sensitive applications such as sequencing, cloning, transfection, or quantitative PCR, follow the assay requirements and consider confirming concentration with an orthogonal method. This tool supports quick planning and transparent arithmetic, while instrument quality and sample preparation remain essential to reliable quantification.

DNA concentration examples

Worked absorbance calculations using standard conversion factors.

Sample	Calculated result	Method
dsDNA, A260 0.5, dilution 10, volume 20 µL	250 ng/µL; 5,000 ng total	Uses the dsDNA factor of 50.
RNA, A260 0.8, dilution 2, volume 50 µL	64 ng/µL; 3,200 ng total	Uses the RNA factor of 40.
ssDNA, A260 0.3, dilution 5, volume 30 µL	49.5 ng/µL; 1,485 ng total	Uses the ssDNA factor of 33.

How to calculate DNA concentration

Select double-stranded DNA, single-stranded DNA, or RNA.
Enter the blank-corrected absorbance measured at 260 nanometers.
Enter the dilution factor and original sample volume in microliters.
Select Calculate Concentration to view concentration and total mass.

DNA concentration FAQ

Why do DNA and RNA use different A260 factors?

Their structures and average extinction behavior differ, so equal absorbance does not imply equal mass concentration. The conventional factors approximate those differences for routine measurements.

What dilution factor should I enter?

Enter how many times more concentrated the original is than the measured solution. Mixing one part sample with nine parts buffer creates a tenfold dilution, so enter 10.

Is ng/µL the same numerical value as µg/mL?

Yes, both numerator and denominator change by a factor of one thousand. A result of 50 ng/µL is therefore also 50 µg/mL.

Can A260 distinguish DNA from RNA?

No, both absorb near 260 nanometers and contaminants can contribute too. Use purification controls or a selective fluorescent assay when composition matters.

What if the spectrophotometer reading is outside its linear range?

Dilute the sample until the absorbance falls within the validated range and measure again. Include the full dilution factor so the calculator reconstructs the original concentration.