Last reviewed: 12 October 2026. Every value below is cited to the document that published it (full list under Sources).
This page collects the reference values researchers cite when they judge total RNA quality: absorbance ratios (A260/A280, A260/A230), electrophoresis metrics (28S/18S), and integrity scores (RIN, DV200). Each number is traced to the manufacturer bulletin or peer-reviewed paper that produced it, so you can cite the primary source directly.
Key takeaways
- “A260/A280 ≈ 2.0 means pure RNA” is only a rule of thumb (Thermo Scientific NanoDrop, T009). The number means little unless the measurement solvent is stated.
- An A260/A280 ratio of 1.8–2.1 is indicative of highly purified RNA (Thermo Fisher Ambion, Quantitating RNA). Measure in slightly alkaline buffer such as TE pH 8.0; the same RNA in unbuffered water can read as low as 1.6 (Ambion; Wilfinger et al., 1997).
- ~1.8 is also the DNA benchmark. If buffered RNA sits at the low end of the range, rule out genomic DNA, protein or phenol carryover before calling it pure.
- RNA reads higher than DNA at 260/280 because it contains uracil instead of thymine (T009).
- Expected A260/A230 values for pure nucleic acid are commonly 2.0–2.2 (Thermo Scientific NanoDrop, T042).
- Acidic solutions under-represent the 260/280 ratio by 0.2–0.3; basic solutions over-represent it by 0.2–0.3 (T009).
- Raising measurement pH from about 5.4 to 7.5–8.5 increased RNA A260/A280 from approximately 1.5 to 2.0 (Wilfinger et al., 1997).
- Wilfinger et al. found the most reproducible RNA ratios at pH 8.0–8.5 in 1–3 mM Na2HPO4.
- Low A260/A280 can come from residual phenol or other extraction reagents, or from very low nucleic acid concentration (T042).
- A low A260/A230 can be an artifact: blanking with water when samples are dissolved in TE may give low 260/230 values (T042).
- RIN scores RNA integrity on a scale of 1 (degraded) to 10 (intact) from the full electrophoresis trace (Schroeder et al., 2006).
- Schroeder et al. introduced RIN because the 28S:18S ratio had been shown to be an inconsistent integrity measure.
- A 28S/18S ratio of 2.0 is a historical convention, not a RIN threshold.
- For FFPE RNA, Illumina uses DV200 (% of fragments >200 nt) instead of RIN, and found RIN was not a reliable predictor of library success.
- Illumina TruSeq RNA Exome bands FFPE RNA as high (DV200 >70%), medium (50–70%), low (30–50%) and not recommended (<30%).
RNA quality reference table
| Metric | Reference value | What it tells you | Source |
|---|---|---|---|
| A260/A280 (TE pH 8.0) | 1.8–2.1 = highly purified RNA; low end (~1.8) also matches DNA, so confirm with A260/A230 and a gDNA check | Protein, phenol or gDNA carryover | Ambion tech note; NanoDrop T009 |
| A260/A280 (unbuffered water) | Same RNA reads lower, e.g. 1.60 (DEPC water, pH 5–6) to 1.85 (pH 6–7) | Solvent artifact, not sample quality | Ambion tech note, Table 1 |
| A260/A230 | Commonly 2.0–2.2 | Salts, guanidine, carbohydrates, phenol absorbing at 230 nm | Thermo Scientific NanoDrop T042 |
| pH effect on A260/A280 | ±0.2–0.3 (acidic lower, basic higher) | Same sample, different buffer, different ratio | NanoDrop T009 |
| RNA A260/A280 vs pH | ~1.5 at pH ~5.4 → ~2.0 at pH 7.5–8.5 | Why water-diluted RNA can read low | Wilfinger, Mackey & Chomczynski, BioTechniques 1997 |
| 28S/18S rRNA ratio | 2.0 (historical convention) | Rough integrity check on a gel | Discussed in Schroeder et al. 2006 |
| RIN | 1 (degraded) – 10 (intact) | Integrity from the whole electropherogram | Schroeder et al., BMC Mol Biol 2006 |
| DV200 (FFPE RNA) | >70% high · 50–70% medium · 30–50% low · <30% not recommended | Usable fragment fraction for library prep | Illumina TruSeq RNA Exome reference guide |
What A260/A280 ratio is acceptable for RNA?
“About 2.0” is a rule of thumb, and it is often quoted without the one detail that decides what it means: the solvent. Thermo Fisher (Ambion) gives 1.8–2.1 as indicative of highly purified RNA, measured in slightly alkaline buffer such as TE pH 8.0. Because ~1.8 is also the DNA benchmark, a reading at the low end deserves a check for genomic DNA, protein or phenol before it is called pure. In unbuffered water the same clean RNA can read 1.6–1.85, so a water reading of 2.0 and a TE reading of 2.0 are not equivalent. Always report the blank and diluent with the ratio, and read it together with A260/A230 and an integrity check. More detail: RNA A260/A280 purity guide.
Why does my RNA A260/A280 change between water and TE?
Because the ratio depends on pH and ionic strength. Wilfinger et al. (1997) showed RNA ratios rising from about 1.5 to 2.0 when pH moved from ~5.4 to 7.5–8.5, and recommended measuring at pH 8.0–8.5 in 1–3 mM Na2HPO4. Unbuffered water is often slightly acidic, which pushes the ratio down. Use the same buffer for the blank and the sample.
What A260/A230 ratio is acceptable?
Commonly 2.0–2.2 for pure nucleic acid, and usually higher than the matching 260/280 value (NanoDrop T042). A clearly lower value suggests contaminants that absorb at 230 nm, such as guanidine salts from lysis buffers. Check the blank first: a water blank with TE-dissolved samples can produce low 260/230 on its own.
Is a 28S/18S ratio of 2.0 required?
No. 2.0 is a historical convention. Schroeder et al. (2006) developed RIN because the 28S:18S ratio had proven inconsistent as an integrity measure. A gel is still a fast first look; see 28S/18S rRNA ratio explained and what degraded RNA looks like on a gel.
What RIN do I need?
RIN runs from 1 to 10 and has no single universal cutoff. Sequencing cores and kit manufacturers set their own minimums by application, so confirm the threshold with your provider before you submit samples.
Which metric should I use for FFPE RNA?
DV200, the percentage of RNA fragments longer than 200 nucleotides, calculated from Bioanalyzer or Fragment Analyzer traces. Illumina found RIN values of FFPE samples fell in a narrow range while DV200 varied widely, making DV200 the better predictor. Thresholds differ by kit; the TruSeq RNA Exome bands are listed in the table above.
Sources
- Thermo Fisher Scientific. 260/280 and 260/230 Ratios, NanoDrop Technical Support Bulletin T009 (Rev 5/07).
- Thermo Fisher Scientific. Assessment of Nucleic Acid Purity, NanoDrop Technical Note T042 (Rev 1/11).
- Wilfinger WW, Mackey K, Chomczynski P. Effect of pH and ionic strength on the spectrophotometric assessment of nucleic acid purity. BioTechniques. 1997;22(3):474–481.
- Schroeder A, Mueller O, Stocker S, et al. The RIN: an RNA integrity number for assigning integrity values to RNA measurements. BMC Molecular Biology. 2006;7:3. doi:10.1186/1471-2199-7-3.
- Illumina. Evaluating RNA Quality from FFPE Samples, Technical Note 470-2014-001.
- Illumina. TruSeq RNA Exome Reference Guide (1000000039582).
- Thermo Fisher Scientific (Ambion). Quantitating RNA, technical note.
Need clean RNA that passes these checks? See Changyu Bio RNA/DNA extraction kits or request a quote. You may cite or link this page; please credit “Changyu Bio, RNA Quality Reference Values”. Research Use Only.