Protein Concentration Calculator

Protein Concentration Calculator

Determine protein concentration using spectrophotometer data and protein-specific parameters

Calculate Protein Concentration

Extinction Coefficient: 6.67 M⁻¹cm⁻¹
Molecular Weight: 66.5 kDa
Absorbance at 280nm: 0.667 (1 mg/mL)

Spectrophotometer Data

Measured absorbance value
1 for undiluted

Common Proteins Reference

BSA
ε: 6.67 M⁻¹cm⁻¹
MW: 66.5 kDa
A₂₈₀: 0.667 (1 mg/mL)
Lysozyme
ε: 2.64 M⁻¹cm⁻¹
MW: 14.3 kDa
A₂₈₀: 2.64 (1 mg/mL)
IgG
ε: 13.7 M⁻¹cm⁻¹
MW: 150 kDa
A₂₈₀: 1.37 (1 mg/mL)
Insulin
ε: 1.08 M⁻¹cm⁻¹
MW: 5.8 kDa
A₂₈₀: 1.08 (1 mg/mL)

Concentration Results

Protein Concentration: 0.75 mg/mL
Molar Concentration: 11.3 μM
Total Protein: 75 μg
Purity Check: A₂₈₀/A₂₆₀ = 1.8

Calculation Steps

1. Beer-Lambert Law: A = ε × c × l

2. Solve for concentration: c = A / (ε × l)

3. Apply dilution factor: cstock = cmeasured × DF

4. Convert to mass concentration: cmass = cmolar × MW

Protein Concentration Formulas

Beer-Lambert Law
A = ε × c × l
A = Absorbance
ε = Extinction coefficient
c = Concentration
l = Pathlength
Mass Concentration
cmass = A / (εmass × l)
cmass = mg/mL
εmass = mL·mg⁻¹·cm⁻¹
A = Absorbance at 280nm
l = Pathlength (cm)
Molar Concentration
cmolar = A / (εmolar × l)
cmolar = M or μM
εmolar = M⁻¹·cm⁻¹
A = Absorbance at 280nm
l = Pathlength (cm)

Extinction Coefficient (ε)

The extinction coefficient measures how strongly a protein absorbs light at 280nm. It depends on the number of tryptophan, tyrosine, and cysteine residues in the protein.

🔬 Tryptophan: ~5,500 M⁻¹cm⁻¹
🧪 Tyrosine: ~1,490 M⁻¹cm⁻¹
⚗️ Cysteine: ~125 M⁻¹cm⁻¹
ε ≈ (nTrp × 5500) + (nTyr × 1490) + (nCys × 125)

Pathlength (l)

The pathlength is the distance light travels through the sample. Standard cuvettes have 1cm pathlength, but microvolume instruments use shorter paths.

Standard Cuvette

1.0 cm pathlength

Microvolume

0.1 – 0.5 cm pathlength

96-well Plate

0.3 – 0.7 cm pathlength

Purity Assessment

The A₂₈₀/A₂₆₀ ratio helps assess protein purity and nucleic acid contamination.

Pure Protein: A₂₈₀/A₂₆₀ ≈ 1.8
Nucleic Acid Contamination: A₂₈₀/A₂₆₀ < 1.5
Check Purity: A₂₈₀/A₂₆₀ between 1.5-1.8

Example Calculations

BSA Standard

A₂₈₀ = 0.667

ε = 6.67 M⁻¹cm⁻¹

l = 1.0 cm

c = 0.667 / (6.67 × 1) = 0.1 mM = 6.65 mg/mL

Diluted Sample

A₂₈₀ = 0.25

DF = 10

ε = 2.64 M⁻¹cm⁻¹ (Lysozyme)

c = (0.25 / 2.64) × 10 = 0.95 mg/mL

Microvolume Measurement

A₂₈₀ = 0.8

l = 0.2 cm

ε = 13.7 M⁻¹cm⁻¹ (IgG)

c = 0.8 / (13.7 × 0.2) = 0.29 mg/mL

Molar Concentration

A₂₈₀ = 0.45

ε = 1.08 M⁻¹cm⁻¹ (Insulin)

MW = 5.8 kDa

c = 0.45 / 1.08 = 0.42 mM = 2.4 mg/mL

Measurement Methods

Direct A₂₈₀

Measures absorbance at 280nm using aromatic amino acids

Advantages: Quick, non-destructive, no reagents
Limitations: Requires known extinction coefficient

Bradford Assay

Colorimetric method using Coomassie Brilliant Blue

Advantages: Sensitive, less affected by contaminants
Limitations: Protein-dependent response

BCA Assay

Biuret reaction with bicinchoninic acid

Advantages: Compatible with detergents
Limitations: More expensive reagents

Lowry Assay

Combines biuret reaction with Folin-Ciocalteu

Advantages: Very sensitive
Limitations: Many interfering substances

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Protein Concentration Calculator – Efficient, Accurate Results for Biologists & Biochemists

Simplify your lab workflow: determine protein concentration from absorbance data, molecular weight, dilution factors and more.

Welcome to the Protein Concentration Calculator from Smart Unit Calculator — the ideal tool for students, researchers, lab technicians and anyone in life sciences who needs to accurately determine protein concentration in solution. Whether you’re working with spectrophotometric measurements at 280 nm, preparing reagents for experiments, or analysing results from a standard curve, our calculator makes the process fast and error-free.

🧪 What is Protein Concentration & Why Does It Matter?

Protein concentration (e.g., mg/mL, µg/mL, µM) tells you how much protein is present in a known volume of solution. In molecular biology, biochemistry, and cell biology labs this matters for:

  • Preparing samples and reagents to the correct concentration
  • Normalising protein loads for assays, gels, westerns or enzyme reactions
  • Comparing results across experiments and labs with confidence
  • Calculating molar concentration when molecular weight is known

Accurate calculations are critical — mistakes in conversion can distort results or cause wasted reagents.

🔍 How Does This Calculator Work?

Our tool uses standard formulas that integrate the following inputs:

  • Absorbance at a known wavelength (often 280 nm for protein absorbance) aatbio.com+1
  • Molecular weight of your protein (g/mol) or custom sequence data omnicalculator.com+1
  • Extinction coefficient (ε) or path-length and dilution factor to adjust readings novoprolabs.com+1
  • Dilution factor, if your sample has been diluted before measurement
  • Path length of the cuvette or microplate (usually 1 cm)

Using the Beer-Lambert law (A = ε × c × l) or derived forms, the calculator returns concentration in units such as mg/mL, µg/mL, or µM depending on inputs.

✅ What You Get From This Tool

  • Instant concentration value based on your inputs
  • Conversion between mass‐based (mg/mL) and molarity (µM) units when you supply molecular weight
  • Support for custom proteins or known standards
  • No need to manually work out complex formulas, saving time and reducing error
  • Ideal for use in lab worksheets, reports, or quick sanity checks

👩‍🔬 Who Should Use It?

Perfect for:

  • Graduate or undergraduate biology / biochemistry students preparing lab reports
  • Lab technicians normalising protein concentrations for experiments
  • Researchers in molecular biology, cell biology, proteomics who need swift conversions
  • Instructors creating teaching materials or assignments
  • Anyone working with purified protein samples and requiring accurate concentration data

💡 Common Use Cases

  • Measuring absorbance at 280 nm and converting to mg/mL for a purified protein
  • Converting µg/mL to µM using known molecular weight for enzyme kinetics
  • Diluting a stock solution and calculating the resulting concentration taking dilution factor into account
  • Verifying sample concentration before running SDS-PAGE or western blotting
  • Comparing concentration across different lab aliquots or time points

Start Using the Protein Concentration Calculator

Eliminate the guesswork and generic estimations. Use our tool to get precise concentration calculations in seconds, so you can focus on your science rather than the maths.

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