Interactive Protein Concentration Calculator
Pick a method, enter your values, and calculate instantly.
What is a protein concentration calculator?
A protein concentration calculator helps you quickly determine how much protein is present in a sample. In practical lab work, this matters for nearly everything: loading gels, setting up enzyme assays, preparing standards, or normalizing samples for downstream experiments like Western blotting or mass spectrometry.
This page gives you three common workflows in one place: UV-based concentration using Beer-Lambert law, direct mass/volume concentration, and dilution planning. That means you can move from measurement to preparation without opening multiple tools.
Core formulas used in this calculator
1) Beer-Lambert law (UV absorbance)
When you measure absorbance at a wavelength like 280 nm, concentration is estimated by:
- c = molar concentration (mol/L)
- A = absorbance (unitless)
- ε = extinction coefficient (L·mol⁻¹·cm⁻¹)
- l = path length (cm)
If molecular weight is known, you can convert molar concentration to mass concentration (mg/mL), which is often easier to use for sample prep.
2) Mass/volume concentration
If you already know how much dry protein (or precipitated pellet) you dissolved:
The calculator also reports % w/v and g/L for convenience.
3) Dilution equation
To dilute a stock to a target concentration:
Solve for V1 (volume of stock to use), then add buffer or solvent to reach the final volume V2.
How to choose the right method
- Use UV absorbance when you have a spectrophotometer and a reliable extinction coefficient.
- Use mass/volume when you prepared the sample directly from a known protein mass.
- Use dilution planning when a stock is already quantified and you need a specific working concentration.
Practical tips for better accuracy
Blank correctly
Your blank should match the sample matrix (same buffer, same additives). A poor blank causes systematic error in absorbance-based concentration.
Know your path length
Classic cuvettes are 1 cm, but microvolume systems may use shorter effective path lengths. Enter the correct value to avoid incorrect concentration estimates.
Watch for interfering substances
Nucleic acids, detergents, reducing agents, and particulates can alter absorbance readings. If contamination is likely, verify concentration with an orthogonal method (e.g., BCA or Bradford assay).
Use realistic significant figures
Even if the calculator gives many decimals, lab measurements have uncertainty. Report concentration with sensible precision based on your method and instrument.
Worked mini examples
Example A: UV method
Suppose A = 0.72, ε = 43,824 L·mol⁻¹·cm⁻¹, l = 1 cm. Then c = 0.72 / 43,824 = 1.64×10⁻⁵ M (about 16.4 µM).
Example B: Mass/volume method
If 20 mg protein is dissolved in 4 mL, concentration = 5 mg/mL.
Example C: Dilution planning
From 10 mg/mL stock, prepare 2 mL at 1 mg/mL. V1 = (1 × 2) / 10 = 0.2 mL stock + 1.8 mL buffer.
FAQ
Can I use this for peptides and antibodies?
Yes. The math is the same, but extinction coefficient and molecular weight must match your specific molecule.
What if my target concentration is higher than stock?
A dilution cannot increase concentration. You would need to concentrate the sample (e.g., spin concentrator, lyophilization, or evaporation strategy compatible with your protein).
Is this a replacement for assay kits?
No. This is a calculation tool. Your concentration quality still depends on the quality of your measurements and assumptions.