What extinction coefficients does this tool use?

Standard values: 50 ng/µL·A260⁻¹ for dsDNA, 33 ng/µL·A260⁻¹ for ssDNA, and 40 ng/µL·A260⁻¹ for RNA. These are the widely accepted empirical coefficients used by Thermo NanoDrop and similar instruments.

What is an ideal A260/A280 ratio?

A ratio of ~1.8 indicates pure DNA; ~2.0 indicates pure RNA. Ratios below 1.7 suggest protein or phenol contamination. Ratios above 2.1 can indicate RNA contamination in a DNA sample.

Why does path length matter?

Beer-Lambert law scales linearly with path length. Standard cuvettes use 1 cm. Micro-volume instruments like the NanoDrop use a 0.1 mm (0.01 cm) or 1 mm path — always check your instrument spec and enter the correct value.

Can I use this for RNA concentration?

Yes. Select "RNA (ssRNA)" and the calculator uses the 40 ng/µL per A260 unit coefficient. This is suitable for total RNA, mRNA, and other single-stranded RNA species.

What does the dilution factor field do?

If you measured a diluted sample (e.g., 1:10), enter the dilution factor and the calculator multiplies the result back to give the original stock concentration.

DNA Concentration Calculator

Name: DNA Concentration Calculator
Availability: InStock
Author: Nham Vu

Enter your A260 absorbance reading to calculate DNA or RNA concentration and estimate purity from the A260/A280 ratio.

Absorbance Inputs

Nucleic Acid Type

A260 Absorbance (required)

A280 Absorbance (optional — for purity ratio)

Path Length (cm)

Standard cuvette = 1 cm. NanoDrop 1 mm pedestal = 0.1 cm.

Dilution Factor

Enter 10 if you measured a 1:10 dilution. Leave 1 for undiluted.

Enter absorbance values and click Calculate

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Summary

Enter your A260 absorbance reading to calculate DNA or RNA concentration and estimate purity from the A260/A280 ratio.

How it works

Select the nucleic acid type: dsDNA, ssDNA, or RNA.
Enter the A260 absorbance value from your spectrophotometer.
Optionally enter the A280 reading to calculate the A260/A280 purity ratio.
Set the path length (default 1 cm for standard cuvettes; 0.1 cm for NanoDrop).
The calculator applies Beer-Lambert law with the appropriate extinction coefficient.
Results show concentration in ng/µL, µg/mL, and µM, plus a purity assessment.

Use cases

Quantify genomic DNA after extraction before PCR or sequencing.
Measure RNA concentration after isolation for transcriptomics experiments.
Assess purity of nucleic acid samples using the A260/A280 ratio.
Calculate the amount of ssDNA oligonucleotide in a synthetic primer stock.
Determine concentration from a NanoDrop or cuvette spectrophotometer reading.
Verify DNA yield after gel purification or column cleanup.
Prepare dilutions for library preparation at a known concentration.
Cross-check fluorometric (PicoGreen) vs. UV absorbance measurements.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu