Protein Concentration Calculator
Determine protein levels from UV absorbance measurements
Select your protein to auto-fill parameters, enter absorbance readings, and get concentration results — edit any field for reverse calculations.
Protein selection
Spectrophotometry parameters
Result
Protein concentration calculator: what it does
This calculator estimates protein concentration from UV spectrophotometry data. It’s designed for quick lab workflows: pick a protein preset (or choose Custom), enter your measurement details, and get a concentration in mg/mL.
🔍 Who is this for?Bench scientists, students, and anyone who needs a fast “sanity check” on a UV-based protein quantification result (before planning dilutions, loading gels, or setting up assays).
If you’re also preparing dilutions, our Cell Dilution Calculator can help you plan the next step after you’ve estimated concentration.
Quick start guide (step-by-step)
The fastest way to use this calculator is: choose a protein preset, confirm the fixed constants, then enter your measurement and dilution details.
Pick a protein (or choose Custom)
Selecting a preset fills in the extinction coefficient and molecular weight for you.
Enter your measurement details
Provide the reading from your instrument at the wavelength you used (commonly 280 nm for proteins), plus the cuvette path length.
Set dilution factor
Use 1 for undiluted stock. For a 1:10 dilution, enter 10.
Read the concentration
The calculator returns protein concentration in mg/mL (and keeps the other fields consistent).
Example walk-through (IgG, diluted sample)
- Select IgG preset (ε = 210,000 M⁻¹·cm⁻¹; MW = 150,000 g/mol).
- Path length: 1 cm.
- Dilution factor: 10 (1:10 dilution).
- Enter your instrument reading (measured at ~280 nm).
Tip: If your lab notebook records dilution like “1:5”, the dilution factor is 5.
Understanding the parameters
Extinction coefficient (ε)
A protein-specific constant that tells you how strongly the molecule absorbs UV light at a chosen wavelength (often 280 nm). Presets fill this automatically; for custom proteins, you’ll typically get ε from a datasheet or sequence-based calculator.
Molecular weight (MW)
Used to convert between molar concentration and mass concentration. If you’re working with a purified protein, MW is usually listed on the product spec sheet.
Path length (b)
The distance light travels through your sample. Standard cuvettes are often 1 cm, while microvolume pedestals can be different.
Dilution factor (n)
If you diluted the sample before reading, multiply back to the original concentration. Example: 1:2 dilution → n = 2.
In most workflows, you record an absorbance reading at a wavelength (typically 280 nm). If your result looks wildly high or low, double-check that you’re entering the measurement reading you intended — not just the wavelength.
Real-world examples / use cases
Loading a gel or Western blot
Estimate how much sample volume gives you the target µg of protein per lane.
Preparing assay standards
Back-calculate the concentration you need to mix standards and controls.
Comparing prep-to-prep consistency
Use the same constants and path length to quickly compare batches across days.
Lab report write-ups
Generate a clean “inputs → concentration” summary you can share with teammates.
Pair with dilution planning
Once you have a concentration, plan your next dilution with our Cell Dilution Calculator.
Tips & best practices
If your ε value is specified at 280 nm, make sure your measurement is also taken at 280 nm.
Common mistakes to avoid
- •Mixing up dilution notation (1:10 means dilution factor 10, not 0.1).
- •Forgetting that path length might not be 1 cm on microvolume instruments.
- •Using a protein preset when your sample is a different species/construct (ε and MW can change).
🧠 A quick sanity check: if your calculated concentration is unexpectedly huge, re-check whether the value you entered is the actual measurement reading you intended.
Calculation method (Beer–Lambert style)
The idea comes from the Beer–Lambert relationship between absorption, path length, and concentration. This calculator uses the following practical form to report protein concentration in mg/mL:
Protein concentration
C = (A / (ε × b)) × MW × n
Where C is concentration (mg/mL), A is the measurement reading at your chosen wavelength, ε is the extinction coefficient,b is path length (cm), MW is molecular weight (g/mol), and n is dilution factor.
Extinction coefficient & molecular weight (presets)
The presets below are provided for convenience when you need a quick estimate. For high-stakes work, always verify constants from your datasheet or a trusted database.
| Substance | MW (g/mol) | ε (M⁻¹·cm⁻¹) |
|---|---|---|
| IgG – Immunoglobulin G | 150,000 | 210,000 |
| BSA – Bovine Serum Albumin | 66,463 | 43,824 |
| Lysozyme | 14,000 | 37,901 |
| Insulin | 5,734 | 6,335 |
| APC – Allophycocyanin | 105,000 | 700,000 |
| PE – Phycoerythrin | 240,000 | 1,960,000 |
| Streptavidin | 55,000 | 176,000 |
| RNAse A | 13,700 | 9,440 |
| Phenylalanine (PHE) | 165.19 | 200 |
| Cysteine (CYS) | 121.16 | 120 |
| Tyrosine (TYR) | 181 | 1,280 |
| Tryptophan (TRP) | 204.23 | 5,690 |
Data shown here mirrors the calculator’s built-in presets. Validate constants against your specific construct and buffer conditions.
FAQs
How do I measure protein concentration?
Common options include UV spectrophotometry (often near 280 nm), dye-based assays (Bradford), and metal-ion based assays (BCA). UV is fast and non-destructive, but it depends on having the right constants.
What dilution factor should I enter?
Use the multiplier relative to the original stock. Example: 1:5 dilution → enter 5. If you’re unsure, use our Cell Dilution Calculator.
Why does the path length matter?
Light absorption increases with how far light travels through the sample. If your instrument uses a path length other than 1 cm, entering the correct value prevents systematic over- or under-estimation.
How do I convert mg/mL to µg/mL?
Multiply by 1000. Example: 2 mg/mL = 2,000 µg/mL.
What if my protein isn’t listed?
Choose Custom protein and enter your own extinction coefficient and molecular weight. This is especially important for fusion proteins, truncations, or non-standard constructs.
Can I share my calculation with a teammate?
Yes. Use the Share button to generate a link. If you check “share with results,” the link includes your inputs and the calculator state.
Limitations & sources
- •Results depend on correct extinction coefficient, molecular weight, and path length.
- •Buffer composition, contaminants (e.g., nucleic acids), and scattering can bias UV-based estimates.
- •This tool is for educational and planning use — it does not replace validated lab SOPs.
External references / further reading
- •Beer–Lambert law (overview)
- •Gill, S. C., & von Hippel, P. H. (1989). Calculation of protein extinction coefficients from amino acid sequence data. Analytical Biochemistry, 182(2), 319-326.
- •Biosyn. (n.d.). How are extinction coefficients determined for proteins?
Links are provided for background reading. Always follow your lab’s protocols and instrument documentation.
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