Protein work often moves back and forth between mass, moles, molecule count, and molar concentration. This calculator helps connect those units quickly when you know the protein molecular weight, whether you are preparing a stock solution, planning an assay, comparing yields, or converting a concentration from mg/ml into µM for experimental design.
Converts a known mass of protein into the equivalent number of moles (or molecules) using the formula:
n (mol) = m (g) ÷ MW (g·mol-1)
Suppose you purified 1 mg of E. coli RpsA protein, which has a molecular weight of 61.2 kDa. How many moles does that correspond to?
n = 1 × 10-3 g ÷ 61,200 g·mol-1
n = 1.634 × 10-8 mol
n = 16.34 nmol
In other words, 1 mg of E. coli RpsA is equivalent to 16.34 nmol of protein.
Converts a known molar amount of protein into the equivalent mass using the same molecular weight.
m (g) = n (mol) × MW (g·mol-1)
Suppose you have 1 nmol of E. coli RpsA protein with a molecular weight of 61.2 kDa. What mass does that correspond to?
m = 1 × 10-9 mol × 61,200 g·mol-1
m = 6.12 × 10-5 g
m = 61.2 µg
In other words, 1 nmol of E. coli RpsA is equivalent to 61.2 µg of protein.
Converts a protein mass in a known volume into molar concentration.
concentration (M) = moles ÷ volume (L)
Suppose you have 1 µg of E. coli RpsA protein in 1 µl, and the protein molecular weight is 61.2 kDa. What molar concentration is that?
n = 1 × 10-6 g ÷ 61,200 g·mol-1
n = 1.634 × 10-11 mol
concentration = 1.634 × 10-11 mol ÷ 1 × 10-6 L
concentration = 16.34 µM
In other words, 1 µg of E. coli RpsA in 1 µl is 16.34 µM.
Converts a molar concentration and volume into the protein mass needed.
m (g) = concentration (M) × volume (L) × MW (g·mol-1)
Suppose you want 1 µl of 1 µM E. coli RpsA protein, and the protein molecular weight is 61.2 kDa. What mass of protein is present?
m = 1 × 10-6 mol/L × 1 × 10-6 L × 61,200 g·mol-1
m = 6.12 × 10-8 g
m = 6.12 × 10-2 µg
In other words, 1 µl of 1 µM E. coli RpsA contains 6.12 × 10-2 µg of protein.