DNA Concentration Calculator

Calculate Concentration from A260, Molarity, Copy Number & Yield

Published: November 15, 2025 | Updated: November 15, 2025

Published by: RevisionTown Team

Accurate DNA concentration measurement is fundamental in molecular biology for PCR, cloning, sequencing, and quantitative analyses. This comprehensive calculator uses spectrophotometric absorbance at 260 nm (A260) to determine DNA concentration, assess purity through A260/A280 ratios, convert to molarity, calculate copy numbers, and determine total DNA yield.

Whether you're using NanoDrop, standard spectrophotometers, or other UV-Vis instruments, this tool provides instant calculations with detailed formulas and quality interpretations for your DNA quantification needs.

DNA Concentration Calculator

Calculation Type:

DNA Concentration Formulas

1. Basic A260 Concentration Formula

Calculate DNA concentration from absorbance at 260 nm:

Concentration (µg/mL) = A₂₆₀ × Dilution Factor × 50

Where: A₂₆₀ = absorbance at 260 nm, 50 µg/mL = conversion factor (1 OD unit = 50 µg/mL for dsDNA)

Example: A₂₆₀ = 0.245, dilution 1:50 → Concentration = 0.245 × 50 × 50 = 612.5 µg/mL

2. Beer-Lambert Law

Fundamental relationship between absorbance and concentration:

A = ε × b × c

Where: A = absorbance (unitless), ε = molar extinction coefficient (M^-1cm^-1), b = path length (cm, usually 1 cm), c = concentration (M)

This law states that absorbance is directly proportional to both the concentration of the absorbing species and the path length through the sample.

3. A260/A280 Purity Ratio

Assess DNA purity and detect protein contamination:

Purity Ratio = A₂₆₀ / A₂₈₀

Interpretation:

1.8-2.0: Pure DNA (1.8 typical for dsDNA)
<1.8: Protein contamination present
>2.0: RNA contamination or high pH

4. DNA Molecular Weight Formula

Calculate molecular weight for molarity conversions:

MW (g/mol) = (Length [bp] × 617.96) + 36.04

Where: 617.96 g/mol = average mass per base pair, 36.04 g/mol = correction for phosphate backbone ends

Alternative: Use 650 Da/bp for quick estimates (commonly used approximation)

5. Molarity Conversion Formula

Convert mass concentration to molar concentration:

Molarity (M) = Concentration (g/L) / MW (g/mol)

Conversion: µg/mL to g/L: divide by 1000 | ng/µL to g/L: multiply by 1

6. Copy Number Calculation

Calculate the number of DNA molecules per microliter:

Copies/µL = (Conc. [ng/µL] × 6.022×10²³) / (Length [bp] × 1×10⁹ × 660)

Where: 6.022×10²³ = Avogadro's number, 660 Da = average MW of bp (use 330 for ssDNA, 340 for ssRNA)

7. DNA Yield Formula

Calculate total amount of DNA in your sample:

DNA Yield (µg) = Concentration (µg/mL) × Volume (mL)

Alternative: Yield (µg) = (Concentration [µg/µL]) × Volume [µL], or convert from ng: Yield (µg) = (ng yield) / 1000

How to Use the DNA Concentration Calculator

Step 1: Measure A260 Absorbance

Use a NanoDrop, spectrophotometer, or plate reader to measure absorbance at 260 nm. Ensure samples are properly diluted to get readings between 0.1-1.0 OD for accuracy. Also measure A280 for purity assessment.

Step 2: Select Calculation Type

Choose the appropriate calculation: basic concentration from A260, molarity conversion, copy number determination, or total yield calculation based on your experimental needs.

Step 3: Enter Values

Input your A260 reading, dilution factor, sample volume, and DNA length as required. The calculator shows only relevant fields for your selected calculation type.

Step 4: Interpret Results

Review calculated concentration, purity ratios, molarity, copy numbers, or yield. The calculator provides quality assessments and recommendations based on standard molecular biology criteria.

DNA Quantification Guidelines

Optimal A260 Range

Target: 0.1 - 1.0 OD units for accurate measurements. Values outside this range should be diluted or concentrated. Most spectrophotometers are most accurate in the 0.1-1.0 range.

Sample Preparation

Use clean, nuclease-free water or appropriate buffer (TE, Tris-HCl). Ensure samples are homogeneous and free of bubbles. Mix gently before measurement to avoid introducing air bubbles.

Dilution Factors

Common dilutions: 1:10, 1:50, 1:100. For highly concentrated samples (>1000 µg/mL), use higher dilutions. Always record and apply the correct dilution factor in calculations.

Blank/Baseline Correction

Always blank the instrument with the same buffer used to dissolve DNA. This corrects for buffer absorbance and ensures accurate readings. Re-blank if changing buffers.

Temperature Control

Measure at consistent temperature (typically 20-25°C). Temperature affects absorbance readings. Allow samples to equilibrate to room temperature before measurement.

DNA Purity Assessment

A260/A280 Ratio Interpretation

1.8-2.0: Pure DNA suitable for most applications (PCR, sequencing, cloning). Ratio of ~1.8 is standard for pure dsDNA.

<1.8: Protein contamination present. May require additional purification. Can inhibit downstream enzymes.

>2.0: RNA contamination or alkaline pH. Consider RNase treatment or check buffer pH (should be 7.0-8.5).

A260/A230 Ratio

>1.5: Pure DNA free from carbohydrate and salt contamination. Ideal ratio is 1.8-2.2.

<1.5: Contamination with guanidine, phenol, carbohydrates, or chaotropic salts. Re-purify or perform additional washes.

Common Contaminants

Proteins: Absorb at 280 nm, lower A260/A280 ratio. Remove with proteinase K treatment or additional phenol-chloroform extraction.

RNA: Absorbs at 260 nm, raises A260/A280 ratio. Remove with RNase A treatment followed by re-purification.

Salts/Solvents: Absorb at 230 nm, lower A260/A230 ratio. Remove with additional ethanol washes or dialysis.

Calculation Examples

Example 1: Basic Concentration from NanoDrop

Given: A₂₆₀ = 0.352, Dilution = 1:25, A₂₈₀ = 0.195

Concentration Calculation:

Concentration = 0.352 × 25 × 50 = 440 µg/mL

Purity Check:

A260/A280 = 0.352 / 0.195 = 1.81 → Pure DNA ✓

Example 2: Molarity Conversion

Given: DNA concentration = 500 µg/mL, Length = 3000 bp

Molecular Weight:

MW = (3000 × 617.96) + 36.04 = 1,853,916 g/mol

Convert to g/L: 500 µg/mL = 0.5 g/L

Molarity:

M = 0.5 / 1,853,916 = 2.70 × 10^-7 M = 270 nM

Example 3: Copy Number Calculation

Given: Concentration = 50 ng/µL, Plasmid length = 5500 bp

Formula:

Copies/µL = (50 × 6.022×10²³) / (5500 × 1×10⁹ × 660)

Copies/µL = 3.011×10²⁵ / 3.63×10¹⁵

Copies/µL = 8.29 × 10⁹ = 8.29 billion copies/µL

Example 4: DNA Yield Calculation

Given: Concentration = 125 µg/mL, Total volume = 200 µL

Convert volume: 200 µL = 0.2 mL

DNA Yield:

Yield = 125 µg/mL × 0.2 mL = 25 µg

Total DNA extracted = 25 µg

DNA Quantification Methods Comparison

Method	Principle	Sample Required	Advantages
A260 (UV Spec)	Absorbance at 260 nm	50-100 µL	Fast, non-destructive, inexpensive
NanoDrop	Micro-volume A260	1-2 µL	Minimal sample, purity info
Fluorometry (Qubit)	Fluorescent dye binding	1-20 µL	DNA-specific, no RNA interference
Gel Electrophoresis	Visual comparison	5-10 µL	Shows DNA integrity

Frequently Asked Questions

How do you calculate DNA concentration from A260?

Use the formula: DNA Concentration (µg/mL) = A260 × dilution factor × 50 µg/mL. This is based on the principle that an A260 of 1.0 corresponds to approximately 50 µg/mL of double-stranded DNA. Always account for any dilutions made before measurement.

What is the A260/A280 ratio and what does it indicate?

The A260/A280 ratio assesses DNA purity. Pure DNA has a ratio of 1.8-2.0 (typically 1.8 for dsDNA). Ratios below 1.8 indicate protein contamination, while ratios above 2.0 may indicate RNA contamination or alkaline conditions.

How do you convert DNA concentration to molarity?

First calculate molecular weight: MW = (length in bp × 617.96 g/mol) + 36.04 g/mol. Then use: Molarity (M) = Concentration (g/L) / MW (g/mol). For example, convert µg/mL to g/L by dividing by 1000.

How do you calculate DNA copy number?

Use the formula: Copy number/µL = (Concentration [ng/µL] × 6.022×10²³) / (Length [bp] × 1×10⁹ × 660). Where 6.022×10²³ is Avogadro's number and 660 Da is the average molecular weight of a base pair.

What is DNA yield and how is it calculated?

DNA yield is the total amount of DNA in your sample. Calculate it using: DNA Yield (µg) = Concentration (µg/mL) × Total Volume (mL). This tells you how much DNA you've extracted or purified from your sample.

Why does A260 measure DNA concentration?

DNA bases (especially purines) absorb ultraviolet light maximally at 260 nm wavelength. This property, described by the Beer-Lambert Law, allows spectrophotometric quantification where absorbance is directly proportional to DNA concentration.

What's the difference between µg/mL and ng/µL?

They are equivalent units. 1 µg/mL = 1 ng/µL. Both represent the same concentration and can be used interchangeably in calculations. Use whichever unit matches your instrument's output or experimental protocol.

Why is my A260/A280 ratio too low?

Ratios below 1.8 typically indicate protein contamination. This can result from incomplete protein removal during extraction, phenol carryover, or improper purification. Perform additional proteinase K treatment or phenol-chloroform extraction to improve purity.

Tips for Accurate DNA Quantification

1. Use Appropriate Dilutions

Keep A260 readings between 0.1-1.0 for best accuracy. Over-concentrated samples give inaccurate readings due to detector saturation.

2. Clean Cuvettes/Pedestals Thoroughly

Residue from previous samples causes inaccurate readings. Wipe NanoDrop pedestals with lint-free wipes and rinse cuvettes with distilled water.

3. Measure Immediately After Preparation

DNA concentration can change over time due to degradation or evaporation. Take measurements promptly for accuracy.

4. Check Full Spectrum (230-320 nm)

Review the complete absorbance spectrum to identify unusual peaks that indicate contaminants (phenol at 270 nm, proteins at 280 nm).

5. Verify with Alternative Methods

Confirm critical samples with fluorometry (Qubit) or gel electrophoresis, especially for NGS, cloning, or qPCR applications.

6. Store DNA Properly

Keep DNA at -20°C or -80°C for long-term storage. Store at 4°C for short-term use. Avoid repeated freeze-thaw cycles.

Master DNA Quantification for Success

Accurate DNA concentration measurement is the foundation of successful molecular biology experiments. This calculator simplifies complex calculations for A260-based quantification, molarity conversions, copy number determinations, and yield assessments. Whether you're setting up PCR reactions, preparing sequencing libraries, or quantifying plasmid DNA, precise concentration measurements ensure reproducible results.

Use this tool alongside quality control measures like purity ratio assessment and gel electrophoresis to validate your DNA samples. Remember that calculated values are starting points—always verify critical samples with multiple methods and maintain proper controls throughout your experiments. For specialized applications requiring high precision, consider fluorometric methods or quantitative PCR for absolute quantification.

If you’re about to send your sample to a laboratory or happen to be simply interested in microbiology, the DNA concentration calculator might just come in handy. What’s even better, it works for RNA and the oligo sequences as well!

We also strongly encourage you to read on if you wish to satisfy your thirst for knowledge. In this article, you will learn about DNA and RNA quantification, the average molecular weights of nucleotides, how to calculate DNA concentration from A₂₆₀, and how to deal with oligonucleotides.

Spectrophotometric analysis of nucleic acids — DNA and RNA quantification

DNA and RNA quantification is usually performed prior to any experiments to determine the concentration and purity of the sample. Many reactions (such as PCR: we made a tool about it: the annealing temperature calculator) involving nucleic acids have specific requirements regarding these two values, so determining them is necessary to obtain the expected results. The amount of added reagents also depends on the initial sample concentration.

The most popular methods of quantification are:

Spectrophotometric analysis of nucleic acids, which works by measuring the UV absorbance of the substance to give you an idea of its concentration and if there are any contaminants. It doesn’t require any additional reagents, but it can’t distinguish between DNA and RNA and has limited sensitivity at low concentrations.
UV fluorescence tagging, which uses dyes that fluoresce when they bind with nucleic acid. This method is more time-consuming and requires a set of known samples for comparison, but it’s also more sensitive.
Agarose gel electrophoresis, which is more complex, but it can also tell you if your sample is intact. It doesn’t rely on checking the DNA absorbance. Instead, it uses agarose gel containing ethidium bromide and samples of known concentration for comparison. Then, a UV light is used to photograph the gel, and you can compare fluorescence intensities and estimate the concentrations.

DNA concentration calculator is meant to help you analyze the results of the spectrophotometry.

How to calculate the DNA concentration from A₂₆₀?

Luckily, if you’re dealing with a standard sample, gathering data from the spectrophotometric analysis of nucleic acids is probably the most challenging part. After that, all you need to do is use the following formula derived from the Beer-Lambert Law:

C = \frac{A_{260}}{l} \times CF \times DF

where:

$C$
– Concentration of the nucleic acid in the sample.
$A_{260}$
– The maximum absorbance as indicated by the spectrophotometric reading. This usually occurs at the wavelength of 260 nm, but it may change depending on the nucleotide. So, if you wondered, why is 260 nm used for DNA?, this is the answer.
$l$
– Pathlength, and more precisely, the length of the cuvette used. The standard value is 1 cm, but your instrument may use a different size.
$DF$
– Dilution factor. It applies only when the sample is diluted. For instance, if you diluted 1 liter of sample in 50 liters of H₂O, the dilution factor would be 50. The dilution factor calculator can help you determine the right value.
CF
– Conversion factor, which depends on the sample type:
- 33 µg/mL for single-stranded DNA (ssDNA);
- 50 µg/mL for double-stranded DNA (dsDNA); and
- 40 µg/mL for RNA.

The most popular concentration units are μg/mL, ng/mL, and mg/mL. After learning how to calculate DNA concentration from A₂₆₀, let’s do the same for other sample types.

How to compute the oligonucleotide sequence concentration?

Oligonucleotides are short, synthetic strands of DNA or RNA that have a number of applications in microbiology. Because they also can be used in processes such as PCR, it’s sometimes useful to be able to calculate their concentration. This value is obtained from the equation:

C = \frac{A_{260}}{ε_{260} \times l} \times MW \times DF

where:

$ε_{260}$

– Extinction coefficient; and
$MW$

– Molecular weight.

The concentration units are like in the previous case. As you may have noticed, the conversion factor was replaced by

\frac{molecular weight}{extinction coefficient}

$extinction coefficient molecular weight$ . Unfortunately, because oligos are short and can be made up of different nucleotides, estimates aren’t accurate. Therefore,
these have to be computed manually – we will take you through the steps below.

Average molecular weight of a nucleotide

To find the total molecular weight of your oligo sequence, you simply need to sum up the atomic weights of all nucleotides in it. You may have to adjust the value depending on its type:

DNA without 5′ monophosphate present — This is an oligo sequence without any modifications. To account for the removal of HPO₂ and the addition of two hydrogens, subtract 61.96 Da for ssDNA or 123.38 Da for dsDNA.
DNA with 5′ monophosphate present — To include 5′ monophosphate left by restriction enzymes, add 17.04 Da for ssDNA or 34.08 Da for dsDNA.
RNA with a 5′ triphosphate — To account for the 5′ triphosphate, add 159.0 Da.

The unit used is Dalton, 1 Da ≈ 1 g/mol.

Below, we present the table of values you can use for the calculation:

Nucleotide	ssDNA [Da]	dsDNA [Da]	RNA [Da]
Adenine	313.21	616.78	329.21
Guanine	329.21	617.88	345.21
Cytosine	289.18	617.88	305.18
Thymine	304.20	616.78	N/A
Uracil	N/A	N/A	306.20

So, for instance, if you tested an unmodified ssDNA oligo sequence AGGTC, its molecular weight would be:

313.21 + 2 × 329.21 + 304.2 + 289.18 − 61.96 = 1503.05 g/mol.

How to calculate the extinction coefficients of DNA and RNA oligo sequences?

The extinction coefficient of a material describes how strongly it absorbs light. This quantity is a bit tricky despite being a rather simple addition. This is because the sum depends not only on the component nucleotides but also on their order. So, how to calculate the extinction coefficient of your oligo sequence? Use the nearest neighbor model:

\begin{array}{r} ε_{260} = \sum_{i = 1}^{N - 1} ε_{nearest neighbor} - \\ \sum_{i = 2}^{N - 1} ε_{individual bases} \end{array}

where:

$ε_{260}$
– Extinction coefficient of the oligo sequence at 260 nm;
$\sum_{i = 1}^{N - 1} ε_{nearest neighbor}$
– Sum of the extinction coefficients of all adjacent pairs of nucleotides; and
$\sum_{i = 2}^{N - 1} ε_{individual bases}$
– Sum of the extinction coefficients of individual nucleotides, excluding the first and the last ones.

The appropriate values can be obtained from the tables below. The units used are M^-1 cm^-1, where M stands for molarity.

🔎 If you’re interested in learning more about molarity, consider visiting our molarity calculator.

Nearest neighbor values:

5’/3′ position	Adenine	Guanine	Cytosine	Thymine	Uracil
Adenine	27,400	25,000	21,200	22,800	24,600
Guanine	25,200	21,600	17,600	20,000	20,000
Cytosine	21,200	18,000	14,600	15,200	17,200
Thymine	23,400	19,000	16,200	16,800	N/A
Uracil	24,000	21,200	16,200	N/A	19,600

Here 5’/3′ position relates to the fact that each end of the DNA molecule has a number. The 5′ carbon has a phosphate group attached to it, the 3′ – carbon-hydroxyl group. DNA is read in from 5′ to 3′ direction.

Individual bases:

Adenine	Guanine	Cytosine	Thymine	Uracil
15,400	11,500	7,400	8,700	9,900

This may seem complicated, so let us continue the example of ssDNA oligo sequence AGGTC. It consists of 4 pairs: AG, GG, GT, and TC. Therefore, the sum of

ε_{nearest neighbor}

is:

\begin{array}{r} \sum_{i = 1}^{N - 1} ε_{nearest neighbor} = 25, ⁣ 200 + \\ 21, ⁣ 600 + 19, ⁣ 000 + 15, ⁣ 200 \\ = 81, ⁣ 000 M^{- 1} {cm}^{- 1} \end{array}

The individual bases to be considered are G, G, and T. Hence:

\begin{array}{r} \sum_{i = 2}^{N - 1} ε_{individual bases} = 2 \times 11, ⁣ 500 + \\ 8, ⁣ 700 = 31, ⁣ 700 M^{- 1} {cm}^{- 1} \end{array}

This yields the extinction coefficient:

\begin{aligned} ε_{260} & = 81, ⁣ 000 - 31, ⁣ 700 \\ = 49, ⁣ 300 M^{- 1} {cm}^{- 1} \end{aligned}

Since we have already calculated the molecular weight (1503.05 g/mol), if we assume the DNA absorbance to be 4,900, no dilution, and standard cuvette size, we can calculate the concentration. Inputting these values into the DNA concentration calculator gives the final result of 149.39 mg/mL.

FAQs

What is a good DNA concentration?

It can be anything between 10 and 300 ng/µL, but there is no set value, and you should check with your laboratory. The DNA concentration required will depend on the following:

Sensitivity of the sequencing machine;
Sample size and volume; and
Sample type. For example, PCR products need less concentration than Plasmids.

What is OD₂₆₀?

OD₂₆₀ stands for the optical density at the wavelength of 260 nm, which measures the reduction in light transmittance caused by scattering. The slower the light is able to travel through a substance, the higher its OD₂₆₀ is. It’s related to the absorbance, A₂₆₀, as follows:

OD₂₆₀ = A₂₆₀ × volume [ml] / pathlength [cm].

How to calculate the DNA concentration from OD₂₆₀?

You can calculate the DNA concentration using the formula:

concentration [μg/mL] = OD₂₆₀ × conversion factor

The conversion factor converts the optical density into concentration and has a fixed value for dsDNA, ssDNA, and RNA.

How to calculate the DNA yield from concentration?

To find the DNA yield from its concentration, use the following equation:

DNA yield [µg] = DNA concentration [μg/mL] × total sample volume [mL].

DNA yield also depends on the quality, freshness, and type of the sample (e.g., saliva or blood).

What does the 260/280 ratio mean?

It is the ratio of the sample absorbance at the wavelengths of 260 and 280 nm. It is used as a measure of the purity of a nucleic acid sample. For pure DNA, the accepted value is ~1.8, whereas for RNA, it’s typically ~2.0.

How to calculate the 260/280 ratio?

To find the 260/280 ratio, proceed as follows:

Measure the absorbance of the sample at the wavelength of 260 nm (A₂₆₀).
Measure the absorbance of the sample at the wavelength of 280 nm (A₂₈₀).
Divide A₂₆₀ by A₂₈₀ to obtain the ratio.

Why is 260 nm used for DNA?

Nucleic acids absorb UV light at a specific wavelength. For DNA and RNA, the maximum absorbance occurs at 260 nm. For comparison, at 280 nm, this value is approximately halved.

DNA Concentration Calculator

Results:

DNA Concentration Formulas

1. Basic A260 Concentration Formula

2. Beer-Lambert Law

3. A260/A280 Purity Ratio

4. DNA Molecular Weight Formula

5. Molarity Conversion Formula

6. Copy Number Calculation

7. DNA Yield Formula

How to Use the DNA Concentration Calculator

Step 1: Measure A260 Absorbance

Step 2: Select Calculation Type

Step 3: Enter Values

Step 4: Interpret Results

DNA Quantification Guidelines

Optimal A260 Range

Sample Preparation

Dilution Factors

Blank/Baseline Correction

Temperature Control

DNA Purity Assessment

A260/A280 Ratio Interpretation

A260/A230 Ratio

Common Contaminants

Calculation Examples

Example 1: Basic Concentration from NanoDrop

Example 2: Molarity Conversion

Example 3: Copy Number Calculation

Example 4: DNA Yield Calculation

DNA Quantification Methods Comparison

Frequently Asked Questions

How do you calculate DNA concentration from A260?

What is the A260/A280 ratio and what does it indicate?

How do you convert DNA concentration to molarity?

How do you calculate DNA copy number?

What is DNA yield and how is it calculated?

Why does A260 measure DNA concentration?

What's the difference between µg/mL and ng/µL?

Why is my A260/A280 ratio too low?

Tips for Accurate DNA Quantification

1. Use Appropriate Dilutions

2. Clean Cuvettes/Pedestals Thoroughly

3. Measure Immediately After Preparation

4. Check Full Spectrum (230-320 nm)

5. Verify with Alternative Methods

6. Store DNA Properly

Master DNA Quantification for Success

Spectrophotometric analysis of nucleic acids — DNA and RNA quantification

How to calculate the DNA concentration from A₂₆₀?

How to compute the oligonucleotide sequence concentration?

Average molecular weight of a nucleotide

How to calculate the extinction coefficients of DNA and RNA oligo sequences?

What is a good DNA concentration?

What is OD₂₆₀?

How to calculate the DNA concentration from OD₂₆₀?

How to calculate the DNA yield from concentration?

What does the 260/280 ratio mean?

How to calculate the 260/280 ratio?

Why is 260 nm used for DNA?

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