mg/mL to molarity calculator

The conversion starts with 1 mg/mL = 1 g/L

Both numerator and denominator change by a factor of 1,000, so the number stays the same. Divide this grams-per-liter concentration by the solute's molar mass in grams per mole:

OpenStax defines molarity using moles of solute per liter of final solution. The denominator is not a liter of solvent before mixing. Here, the mg/mL input already supplies the final-volume basis.

Worked example: 2 mg/mL and 200 g/mol

For an illustrative solute with a molar mass of 200 g/mol, a concentration of 2 mg/mL is 2 g/L. Dividing 2 by 200 gives 0.01 mol/L, which is 10 mmol/L or 10,000 µmol/L.

In reverse, 10 mmol/L = 0.01 mol/L. Multiplying by 200 g/mol gives 2 g/L, or 2 mg/mL. These are arithmetic inputs, not a recommended concentration.

M, mM and µM are different scales

The SI prefixes milli and micro mean one thousandth and one millionth. For example, a numerical value in mM is 1,000 times the same concentration expressed in M. The uppercase M is used here for mol/L; it is not the lowercase m sometimes used for molality.

Match the molar mass to the reported concentration

A chemical's free form, salt and hydrate may have different molar masses. If a concentration is reported as an amount of one component or “equivalent to” another form, its mass basis must match the molar mass you enter. Do not combine the mass concentration of an entire salt with the molar mass of only one part of it.

Look for a molar mass in g/mol in the information for the actual material. A bare molecular-weight number is insufficient if you do not know what chemical form it describes. IUPAC defines molar mass as mass divided by amount of substance; the g/mol unit makes the intended quantity explicit.

Why the same mg/mL can give different molarity

At 2 mg/mL, a molar mass of 200 g/mol gives 10 mM, while 400 g/mol gives 5 mM. The same mass contains fewer moles when each mole has more mass. This is why there is no universal fixed mg/mL-to-M factor.

Choose the appropriate starting tool

• If the label says mg per 5 mL or another paired ratio, first use the concentration label converter.
• For a confirmed mass-per-volume percentage, use the % w/v to mg/mL converter first.
• If you need a volume corresponding to an already specified mass, use the main mg to mL calculator with your concentration.

This page requires the concentration of one identified solute. It does not infer a molar mass for mixtures, estimate speciation after a reaction, or use whole-solution density as an ingredient concentration.

See all concentration tools →