Protein Concentration Calculator

Guessing your protein concentration is not a lab strategy. It's a way to waste reagents, time, and entire experiments.

The protein concentration calculator takes your spectrophotometric absorbance reading and sample parameters — extinction coefficient, molecular weight, pathlength, and dilution factor — and delivers your exact protein concentration in mg/mL in seconds.

No manual Beer-Lambert calculations. No unit conversion errors. Just accurate results before your next pipetting step.

What Is Protein Concentration?

Protein concentration is the measure of the total amount or mass of protein present within a given volume of solution — typically expressed in:

• mg/mL (milligrams per milliliter) — most common in lab settings

• M (molarity) — moles of protein per liter of solution

• µg/µL (micrograms per microliter) — used for lower concentration samples

It is a fundamental measurement in biochemistry, biotechnology, and diagnostics — used to quantify protein expression levels, validate purification yield, and ensure experimental consistency.

Common Applications of Protein Concentration Measurement

• Protein purification — monitoring yield at each step of separation

• Research and development — normalizing samples for fair experimental comparisons

• Clinical diagnostics — measuring protein levels in blood, tissue lysates, or biological fluids

• Industrial manufacturing — real-time monitoring during large-scale protein production

• Western blots and enzymatic assays — ensuring correct protein loading amounts

The Beer-Lambert Law — Formula Behind the Calculator

The protein concentration calculator uses the Beer-Lambert Law — the gold standard for spectrophotometric protein quantification:

C (mol/L) = A ÷ (ε × l)

To convert to mg/mL:

C (mg/mL) = (A × MW × Dilution Factor) ÷ (ε × l)

Where:

• A = Absorbance at λmax (unitless)

• ε = Extinction coefficient (M⁻¹ cm⁻¹)

• l = Pathlength (cm)

• MW = Molecular weight (g/mol)

• Dilution Factor = how much the sample was diluted before measurement

How the Protein Concentration Calculator Works

Inputs

• Protein — select from dropdown (e.g., IgG — Immunoglobulin G) or enter custom protein

• Extinction coefficient (ε) — auto-filled based on protein selection (e.g., IgG = 2,10,000 M⁻¹ cm⁻¹)

• Molecular weight — auto-filled based on protein (e.g., IgG = 1,50,000 g/mol)

• Absorbance at λmax — your spectrophotometer reading in nm

• Pathlength — default 1 cm (standard cuvette length)

• Dilution factor — default 1 (adjust if sample was pre-diluted)

Output

• Concentration — displayed in mg/mL (auto-calculated)

Select your protein, enter your absorbance reading, and concentration is calculated instantly.

Extinction Coefficient and Molecular Weight — Reference Table

Different proteins absorb UV light differently — which is why the extinction coefficient is protein-specific and must match your sample type for accurate results.

How to Calculate Protein Concentration — Step by Step

Example 1 — IgG (Immunoglobulin G)

Protein: IgG, A = 0.5, ε = 210,000 M⁻¹cm⁻¹, MW = 150,000 g/mol, Pathlength = 1 cm, Dilution = 1

Step 1 — Calculate molar concentration: C = A ÷ (ε × l) C = 0.5 ÷ (210,000 × 1) C = 2.38 × 10⁻⁶ mol/L

Step 2 — Convert to mg/mL: C = 2.38 × 10⁻⁶ × 150,000 C = 0.357 mg/mL

Example 2 — Diluted Sample

Protein: IgG, A = 0.8, Dilution factor = 5, same parameters

1. C (mol/L) = 0.8 ÷ (210,000 × 1) = 3.81 × 10⁻⁶ mol/L

2. C (mg/mL) = 3.81 × 10⁻⁶ × 150,000 = 0.571 mg/mL

3. Account for dilution: 0.571 × 5 = 2.857 mg/mL

Example 3 — BSA (Bovine Serum Albumin)

A = 0.65, ε = 43,824 M⁻¹cm⁻¹, MW = 66,463 g/mol, Pathlength = 1 cm, Dilution = 1

1. C = 0.65 ÷ (43,824 × 1) = 1.483 × 10⁻⁵ mol/L

2. C = 1.483 × 10⁻⁵ × 66,463 = 0.985 mg/mL

Fun Fact That'll Make You Laugh 😄

IgG — Immunoglobulin G is the most abundant antibody in human blood — making up about 75% of all serum antibodies.

It's also the most studied, most purified, and most calculated protein in biochemistry labs worldwide.

So when scientists developed a default protein for spectrophotometry calculators — of course they picked the one that's literally in everyone's blood.

Your immune system is basically the periodic table's carbon of the protein world. 😂

Frequently Asked Questions

What is an extinction coefficient?

The extinction coefficient (ε) is a measure of how strongly a protein absorbs light at a specific wavelength — expressed in M⁻¹ cm⁻¹. It is protein-specific and determined by the amino acid composition, particularly tryptophan and tyrosine residues. A higher extinction coefficient means the protein absorbs more light per unit concentration, making it easier to detect spectrophotometrically.

What is IgG Immunoglobulin G?

IgG (Immunoglobulin G) is the most abundant antibody class in human serum — making up approximately 75% of all antibodies in blood. It plays a central role in immune defense against bacteria and viruses. In the lab, IgG is one of the most commonly purified and quantified proteins, with an extinction coefficient of 210,000 M⁻¹ cm⁻¹ and molecular weight of 150,000 g/mol.

What is absorbance at λmax?

Absorbance at λmax is the measurement of how much light your protein sample absorbs at its peak absorption wavelength. For most proteins, λmax is 280 nm — the wavelength where tryptophan and tyrosine residues absorb UV light most strongly. This reading is taken directly from a spectrophotometer and is the primary input for Beer-Lambert Law concentration calculations.

How does dilution factor affect protein concentration?

The dilution factor accounts for any pre-dilution of your sample before measurement. If your sample was diluted 10× before reading absorbance, enter 10 as the dilution factor — the calculator multiplies your calculated concentration by this value to give you the true original concentration. Forgetting to account for dilution is one of the most common sources of error in protein quantification.

What is Beer-Lambert Law in protein concentration?

Beer-Lambert Law states that absorbance is directly proportional to concentration and pathlength: A = ε × l × C. Rearranged for concentration: C = A ÷ (ε × l). It is the mathematical foundation of all spectrophotometric protein quantification — used in every UV-Vis absorbance measurement from simple protein assays to complex purification monitoring.