Beer-Lambert Calculator
A free online Beer-Lambert law calculator that solves A = εlc for any unknown variable — absorbance, molar absorptivity, path length, or concentration. Includes DNA/RNA quantification mode with OD260/OD280 purity ratio assessment, common chromophore presets (NADH, pNP, Bradford), and unit conversion — all calculated in your browser.
Chromophore Presets
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What is the Beer-Lambert Law?
The Beer-Lambert Law (A = εlc) describes the linear relationship between absorbance (A) and the concentration (c) of a light-absorbing substance. Here, ε is the molar absorptivity (extinction coefficient) in L/(mol·cm), and l is the optical path length in cm. This law is fundamental in spectrophotometry for quantifying concentrations of DNA, RNA, proteins, and other molecules in solution.
How to Use This Calculator
- Select what you want to solve for: absorbance, concentration, path length, or molar absorptivity
- Enter the known values in the input fields
- Or switch to DNA/RNA Quantification mode for OD-based nucleic acid concentration
- Select a chromophore preset if applicable (NADH, pNP, Bradford, etc.)
- View the calculated result with step-by-step formula breakdown
- Check transmittance (%T) which is automatically calculated from absorbance
Frequently Asked Questions
What is a good A260/A280 ratio for DNA?
For pure DNA, an A260/A280 ratio of ~1.8 is expected. For pure RNA, a ratio of ~2.0 is expected. Lower ratios indicate protein or phenol contamination, while higher ratios may indicate RNA contamination in DNA samples.
What conversion factor should I use for DNA quantification?
The standard conversion factors are: dsDNA = 50 µg/mL per OD260, ssDNA = 33 µg/mL per OD260, RNA = 40 µg/mL per OD260. These assume a 1 cm path length cuvette.
When does the Beer-Lambert Law fail?
The Beer-Lambert Law is valid for dilute solutions (typically A < 1.0). At high concentrations, deviations occur due to molecular interactions. Also, stray light, fluorescence, and light scattering can cause non-linearity.