DNA Concentration Calculator

The DNA concentration calculator turns the absorbance readings from a UV spectrophotometer or NanoDrop-style instrument into a usable nucleic acid concentration in ng/µL, µg/mL, and mg/mL. You enter the absorbance at 260 nm (A260), the dilution factor, and the cuvette path length, then select whether your sample is double-stranded DNA, single-stranded DNA, RNA, or a short oligonucleotide. The tool instantly returns the concentration and an estimate of total yield for a 100 µL sample.

Beyond quantification, the calculator also reports the two purity ratios that every molecular biology lab relies on: the A260/A280 ratio and the A260/A230 ratio. Nucleic acids absorb most strongly at 260 nm, proteins absorb at 280 nm, and contaminants such as residual phenol, guanidine salts, and EDTA absorb near 230 nm. By comparing these absorbances, the nucleic acid quantification calculator flags whether your prep is clean or carries protein and chaotrope contamination that could ruin downstream PCR, sequencing, cloning, or transfection.

This DNA concentration calculator is built for anyone working with extracted genomic DNA, plasmid minipreps, PCR products, RNA preps, or synthesized oligos. Instead of doing the arithmetic by hand, you get an immediate, repeatable answer that matches the standard convention used by Thermo Fisher, Promega, and Qiagen protocols.

The core of the DNA concentration calculator is the Beer-Lambert relationship applied with a nucleic-acid-specific extinction coefficient. The concentration is the product of the A260 reading, the extinction coefficient, and the dilution factor, divided by the path length. The path length normalizes the reading to a standard 1 cm cuvette, and the dilution factor scales the result back up to the concentration of the original undiluted stock.

Each type of nucleic acid absorbs UV light slightly differently, so the calculator uses a different coefficient for each. The widely accepted convention is that an A260 of 1.0 (in a 1 cm path) corresponds to roughly 50 ng/µL of double-stranded DNA, 33 ng/µL of single-stranded DNA or an oligonucleotide, and 40 ng/µL of RNA. These are exactly the values this tool applies:

• Double-stranded DNA (dsDNA): 50 ng·cm/µL
• Single-stranded DNA (ssDNA): 33 ng·cm/µL
• RNA: 40 ng·cm/µL
• Oligonucleotide: 33 ng·cm/µL

Choosing the correct sample type matters: quantifying single-stranded DNA with the dsDNA coefficient would overstate the concentration by about 50%. The unit conversions are direct because ng/µL is numerically equal to µg/mL, while mg/mL is the concentration divided by 1000.

Concentration alone does not tell you whether a nucleic acid sample is clean. The DNA concentration calculator also computes two diagnostic ratios. The A260/A280 ratio is the A260 reading divided by the A280 reading, and it reports protein contamination. The A260/A230 ratio is the A260 reading divided by the A230 reading, and it reports contamination by salts, carbohydrates, phenol, and other organic compounds carried over from extraction.

For pure double-stranded DNA, an A260/A280 ratio in the 1.7 to 1.9 window is considered clean; a ratio below 1.7 usually signals residual protein, while a high ratio can indicate RNA carryover. For RNA, the target window shifts upward to roughly 1.9 to 2.1. The A260/A230 ratio is interpreted the same way for all sample types: a value between 2.0 and 2.2 indicates a clean prep, and a value below 2.0 points to chaotrope salts, phenol, or EDTA contamination.

A reliable prep should pass both checks. A sample with a great concentration but an A260/A230 of 1.2 may still inhibit enzymatic reactions, which is why this calculator surfaces both ratios alongside the concentration result.

Using the DNA concentration calculator takes only a few seconds once you have your spectrophotometer readings. Follow these steps for an accurate result.

1. Select the nucleic acid type. Choose double-stranded DNA, single-stranded DNA, RNA, or oligonucleotide so the calculator applies the correct extinction coefficient (50, 33, 40, or 33).
2. Enter A260. Type the absorbance reading at 260 nm. Keep readings between roughly 0.1 and 1.0 for the most reliable measurement; dilute concentrated samples to stay in this linear range.
3. Enter A280 and A230. These feed the purity ratios. If your instrument only reports A260, you can still get a concentration, but the ratios will not be meaningful.
4. Set the dilution factor. If you diluted the sample 1:10 before reading, enter 10. For an undiluted sample, leave it at 1.
5. Set the path length. Standard cuvettes use 1 cm. Micro-volume pedestal instruments often use a shorter path such as 0.1 cm or 1 mm, which the calculator divides by.

The result panel shows the concentration in ng/µL, the equivalent µg/mL and mg/mL values, the total yield for a 100 µL sample, and both purity ratios with a plain-language assessment.

Once you know the concentration, the DNA concentration calculator helps you plan the next step by reporting total yield and multiple units. Total yield is the concentration multiplied by your sample volume; this tool assumes a 100 µL sample, so a concentration of 25 ng/µL corresponds to 2500 ng (2.5 µg) of recovered nucleic acid. If your actual volume differs, simply multiply the ng/µL value by your real volume in microliters to get total nanograms.

The unit conversions follow directly from the definitions. Because a microliter is one-thousandth of a milliliter and a nanogram is one-thousandth of a microgram, the numeric value of ng/µL is identical to µg/mL. To express the same concentration in mg/mL, divide by 1000. These conversions are handy because protocols quote target amounts in different units: a cloning reaction might call for nanograms of insert, a transfection might specify µg of plasmid, and a stock solution might be labeled in mg/mL.

Knowing yield up front prevents wasting a precious prep. If you need 1 µg of DNA for a restriction digest and your calculator shows only 0.6 µg total, you know to concentrate the sample or scale down the reaction before pipetting.