mg/mL to Micromolar Calculator: Mass Concentration to µM

This calculator converts a mass concentration into a molar concentration. Enter the concentration in milligrams per millilitre and the molar mass of the dissolved substance; you get the concentration in micromolar (µM), millimolar (mM) and nanomolar (nM).

Formula

c (mol/L) = ρ (g/L) ÷ M, and 1 mg/mL = 1 g/L.

• ρ: mass concentration; mg/mL and g/L are the same number (1 mg/mL = 1000 mg per 1000 mL = 1 g/L)
• M: molar mass in g/mol
• c: molar concentration in mol/L
• 1 mol/L = 10³ mM = 10⁶ µM = 10⁹ nM

Worked Example

A 0.5 mg/mL solution of glucose (M = 180.156 g/mol).

1. 0.5 mg/mL = 0.5 g/L
2. c = 0.5 ÷ 180.156 = 0.002775372 mol/L
3. In micromolar: 0.002775372 × 1,000,000 = 2,775.37 µM
4. In millimolar: 0.002775372 × 1000 = 2.7754 mM; in nanomolar: 0.002775372 × 1,000,000,000 = 2,775,372 nM

Assumptions

• The molar mass is that of the dissolved species as it was weighed, including any counter-ion or water of crystallisation in a salt or hydrate.
• The mass concentration is mass of solute per volume of solution.
• For a large molecule such as a protein, M is its molar mass in g/mol (1 kDa corresponds to 1000 g/mol).

How to read the result

The larger the molar mass, the fewer moles a milligram holds, so the same 0.5 mg/mL is about 2,775 µM for glucose but only about 10 µM for a 50,000 g/mol protein. Use µM for typical working concentrations, mM for stock solutions and nM for very dilute ones. To find the mass needed for a given molarity instead, use the molarity calculator from mass, and the molar mass calculator for M.

Limits and common mistakes

• Confusing mg/mL with µg/mL changes the answer by a factor of 1000.
• Using the molar mass of the free form when you weighed a salt or hydrate overstates the molar concentration.
• Kilodaltons must be converted: 66.5 kDa is 66,500 g/mol, not 66.5.

Frequently Asked Questions

How do I convert mg/mL to µM?

Divide the mg/mL value by the molar mass in g/mol, then multiply by 1,000,000.

What is 0.5 mg/mL of glucose in µM?

About 2,775.37 µM, or 2.775 mM.

Is mg/mL the same as g/L?

Yes. 1 mg/mL equals 1 g/L, so the numbers are identical.

How do I go from µM back to mg/mL?

Multiply µM by the molar mass and divide by 1,000,000.

in x | Mass concentration | mg/mL | 0.5 | 0
in mm | Molar mass | g/mol | 180.156 | 0.001
out um | Concentration in micromolar | µM | x / mm * 1000000 | 2
out cmm | Concentration in millimolar | mM | x / mm * 1000 | 4
out nm | Concentration in nanomolar | nM | x / mm * 1000000000 | 0