A260 Absorbance to Concentration Calculator

Convert UV absorbance at 260 nm (A260) to concentration for dsDNA, ssDNA, or RNA. Tailored for cuvette spectrophotometer measurements with adjustable dilution factors and path lengths.

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Measurement Inputs

Input absorbance, nucleic acid type, and dilutions.

Absorbance at 260 nm (A₂₆₀)

Nucleic Acid Type

Dilution Factor (e.g. 10 for 1:10)

Cuvette Path Length (cm)

Sample Volume (μL, optional for total yield)

Nucleic Acid Concentration

25.0 μg/mL

* Equal to 25.0 ng/μL.

Extinction Constant 50 μg/mL per OD

Total Yield 2.5 μg (2500 ng)

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Linear Dynamic Range

Keep raw spectrophotometer absorbance within 0.1 to 1.0 A260 for valid Beer-Lambert calculations.

A260 Conversion Coefficients & Yield Summary Table

Nucleic Acid Category	Standard A260 = 1.0 Constant	Concentration at A260 = 0.5 (Undiluted)	Total Yield per 100 μL Sample
Double-Stranded DNA (dsDNA)	50 μg/mL (50 ng/μL)	25.0 ng/μL	2.50 μg
Single-Stranded DNA (ssDNA)	33 μg/mL (33 ng/μL)	16.5 ng/μL	1.65 μg
Single-Stranded RNA (ssRNA)	40 μg/mL (40 ng/μL)	20.0 ng/μL	2.00 μg

Calculation Methodology & Equations

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Beer-Lambert Law Application

Conc = (A₂₆₀ × Factor × Dilution) / Path_Length

Absorbance spectroscopy relates light extinction to substance concentration.

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Standard Conversion Constants

At 260 nm wavelength, an optical density (OD) of 1.0 corresponds to standard mass concentrations: dsDNA = 50 μg/mL, ssDNA = 33 μg/mL, RNA = 40 μg/mL.

Frequently Asked Questions

What does A260 measure in spectrophotometry? ▼

A260 measures light absorbance at a wavelength of 260 nm, which corresponds to the maximum UV absorption peak for nucleic acid bases (adenine, guanine, cytosine, thymine, and uil).

Why does path length affect concentration calculations? ▼

According to the Beer-Lambert law ($A = varepsilon cdot c cdot l$), absorbance is directly proportional to path length ($l$). Microvolume spectrophotometers (e.g. NanoDrop) often use 0.1 cm or 0.05 cm path lengths, requiring normalization to a standard 1.0 cm path.

What is the difference between μg/mL and ng/μL? ▼

They are numerically identical mass concentration units: 1 μg/mL = 1 ng/μL (since 1 μg = 1,000 ng and 1 mL = 1,000 μL).