320
ng/µL
0.32
µg/mL
320
ng/µL
0.32
µg/mL
The RNA Concentration Calculator determines RNA concentration from UV absorbance readings at 260 nm. RNA quantification is a critical step before reverse transcription, qRT-PCR, RNA-seq library preparation, and Northern blotting. Unlike DNA, RNA uses an extinction coefficient of 40 ng/µL per absorbance unit, reflecting the different optical properties of ribonucleotides. Enter your A260 reading and dilution factor to get an instant concentration result.
The concentration is calculated using the Beer-Lambert law:
Concentration (ng/µL) = A260 × Dilution Factor × 40
Where:
Note: 1 ng/µL = 1 µg/mL, so the numerical values are the same in both units.
Inputs
Results
An A260 of 0.4 with a 20-fold dilution yields an RNA concentration of 320 ng/µL (320 µg/mL).
Inputs
Results
A direct A260 reading of 0.15 without dilution corresponds to 6 ng/µL of RNA, which may be too low for reliable quantification by spectrophotometry.
RNA is predominantly single-stranded, which means its bases are less stacked compared to the well-ordered double helix of dsDNA. This results in greater UV absorption per mass unit (hyperchromicity). Conversely, the factor is lower (40 vs 50) because more absorption per molecule means fewer ng are needed to produce the same absorbance. The factor reflects that ssRNA absorbs ~25% more per base than dsDNA.
Pure RNA should have an A260/A280 ratio of approximately 2.0 (compared to 1.8 for DNA). A ratio below 1.9 suggests protein contamination, while a ratio significantly above 2.1 may indicate degraded RNA or buffer effects. Note that the pH of the measurement buffer can affect this ratio; slightly alkaline buffers (like TE pH 8.0) give more reproducible results.
No, UV spectrophotometry cannot distinguish between intact and degraded RNA because both absorb equally at 260 nm. To assess RNA integrity, you must use gel electrophoresis (looking for sharp 28S and 18S rRNA bands) or an Agilent Bioanalyzer/TapeStation to obtain an RNA Integrity Number (RIN). A RIN above 7 is generally considered acceptable for most downstream applications.
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