Molar Extinction Coefficient & Beer-Lambert (A = ε·c·l)

Molar Extinction Coefficient & Beer-Lambert (A = ε·c·l) | 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 Molar Extinction Coefficient & Beer-Lambert Calculator solves for any variable in the Beer-Lambert equation (A = ε·c·l)—absorbance, molar extinction coefficient, concentration, or optical path length—with built-in unit conversion for M, mM, µM, nM, cm, and mm.

When to use

Determining unknown solute concentrations from spectrophotometric absorbance readings.
Calculating molar absorptivity (ε) for novel chromophores, proteins, or chemical dyes from standard solutions.
Predicting expected absorbance values or selecting optimal cuvette path lengths for kinetic assays.

How it works

1Select the variable you want to compute (Absorbance, Extinction Coefficient, Concentration, or Path Length).
2Enter the known values and specify the appropriate concentration (M, mM, µM, nM) and path length (cm, mm) units.
3Adjust the output decimal precision to generate the final calculated value and underlying formula substitution.

Use cases

Enzymatic activity assays monitoring NADH or NADPH consumption and production at 340 nm.
Nucleic acid and protein concentration determination via UV absorbance at 260 nm and 280 nm.
Analytical chemistry workflows establishing calibration baselines and characterizing newly synthesized dyes.

Examples

1. Verifying NADH Absorbance in an Enzyme Assay

Biochemist

Background

A researcher is running a dehydrogenase enzyme coupled assay producing 100 µM NADH in a standard 1 cm cuvette.

Problem

Calculate the expected absorbance at 340 nm to confirm whether the assay will fall within the linear range of the spectrophotometer.

How to use

Set Solve For to 'Absorbance (A)', enter Extinction Coefficient as 6220, Concentration as 100 with unit 'uM', and Path Length as 1 with unit 'cm'.

Outcome

Returns an expected absorbance of A = 0.6220.

2. Determining Molar Absorptivity of a Synthetic Fluorophore

Organic Chemist

Background

A chemist synthesizes a dye and prepares a 50 µM standard solution that produces an absorbance of 1.200 in a 1 cm cuvette.

Problem

Determine the molar extinction coefficient (ε) to report in a publication.

How to use

Set Solve For to 'Extinction Coefficient ε (M⁻¹cm⁻¹)', enter Absorbance as 1.2, Concentration as 50 with unit 'uM', and Path Length as 1 with unit 'cm'.

Outcome

FAQ

What is the Beer-Lambert law equation?

The Beer-Lambert law is A = ε·c·l, where A is absorbance (dimensionless), ε is the molar extinction coefficient (M⁻¹cm⁻¹), c is molar concentration (mol/L), and l is the optical path length (cm).

How does the tool handle concentration and path length unit conversions?

Non-standard units such as mM, µM, nM, and mm are automatically converted to M (mol/L) and cm before performing calculations to match the standard dimension of ε (M⁻¹cm⁻¹).

What is the standard extinction coefficient for NADH at 340 nm?

The accepted molar extinction coefficient for NADH at 340 nm is 6,220 M⁻¹cm⁻¹ (6.22 × 10³ M⁻¹cm⁻¹).

Why does absorbance have no units?

Absorbance is defined as the logarithm of the ratio of incident light intensity to transmitted light intensity (log₁₀(I₀/I)), making it a dimensionless value.

Can I solve for concentration when using a microplate reader with a non-standard path length?

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Key facts

Overview

When to use

How it works

Use cases

Examples

1. Verifying NADH Absorbance in an Enzyme Assay

2. Determining Molar Absorptivity of a Synthetic Fluorophore

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