OD260/280 Nucleic Acid Purity Ratio Calculator

OD260/280 Nucleic Acid Purity Ratio Calculator | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Education
Input types: select, number
Output type: json
Sample coverage: 4
API ready: Yes

Overview

The OD260/280 Nucleic Acid Purity Ratio Calculator evaluates DNA or RNA purity from A260 and A280 absorbance readings, with an optional A260/A230 secondary check for organic or salt carryover. It compares the calculated ratios with expected ranges for DNA and RNA and is intended for educational use.

When to use

Check whether a DNA preparation is near the expected A260/A280 ratio of 1.8.
Assess whether an RNA preparation is near the expected A260/A280 ratio of 2.0.
Use A260/A230 as a secondary check for guanidine, phenol, organic, or salt carryover.

How it works

1Select DNA or RNA as the nucleic acid type.
2Enter A260 and A280 readings from the same diluted sample.
3The calculator divides A260 by A280 and compares the result with the selected nucleic acid range.
4Optionally enter A230 to calculate and interpret the A260/A230 ratio, then choose the desired decimal places.

Use cases

Screen plasmid DNA preparations before restriction digestion or sequencing.
Review RNA extraction quality before RT-qPCR.
Teach spectrophotometric purity assessment using realistic absorbance readings.

Examples

1. Clean DNA preparation with an A260/A280 ratio of 1.80

Molecular biology student

Background

A plasmid preparation produced A260 = 0.45 and A280 = 0.25 readings.

Problem

The student needs to determine whether the DNA purity is consistent with the expected ratio.

How to use

Select DNA, enter 0.45 for A260 and 0.25 for A280, enter 0.20 for optional A230, and set decimal places to 2.

nucleicAcidType: DNA; a260: 0.45; a280: 0.25; a230: 0.20; decimalPlaces: 2

Outcome

The calculator returns A260/A280 = 1.80, consistent with clean DNA in the 1.7–2.0 window. A260/A230 = 2.25 does not indicate organic or salt carryover.

2. RNA preparation with low A260/A280 and A260/A230 ratios

RNA extraction researcher

Background

A TRIzol RNA preparation produced A260 = 0.60, A280 = 0.36, and A230 = 0.90.

Problem

The researcher needs to check whether contamination may affect downstream RT-qPCR.

How to use

Select RNA, enter the three absorbance readings, and set decimal places to 4.

FAQ

What does the A260/A280 ratio measure?

It compares absorbance at 260 nm and 280 nm to help assess nucleic acid purity and identify possible protein or phenol contamination.

What is the expected A260/A280 ratio for pure DNA?

Pure DNA is expected to be approximately 1.8, with an acceptable window of about 1.7–2.0.

What is the expected A260/A280 ratio for pure RNA?

Pure RNA is expected to be approximately 2.0, with an acceptable window of about 1.8–2.2.

What does a low A260/A280 ratio indicate?

A low ratio can indicate protein or phenol contamination; interpretation depends on whether the sample is DNA or RNA.

What is the optional A260/A230 check used for?

A low A260/A230 ratio can indicate carryover of guanidine, phenol, organic compounds, or salts. A pure sample is commonly near 2.0–2.2.

nucleicAcidType: RNA; a260: 0.60; a280: 0.36; a230: 0.90; decimalPlaces: 4

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Clean DNA preparation with an A260/A280 ratio of 1.80

2. RNA preparation with low A260/A280 and A260/A230 ratios

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