To convert mM to molar, divide by 1,000; to convert molar to mM, multiply by 1,000. So 10 mM = 0.01 M, 1 mM = 1,000 µM, and 1 µM = 1,000 nM. The converter above handles molar, millimolar, micromolar, nanomolar and picomolar. It also converts mg/mL, µg/mL, g/L and % w/v to molarity once you enter a molar mass, and normality (N) to molarity with the number of equivalents. Pick a common chemical to fill in its molar mass from PubChem.
How to convert mM to molar and molar to mM
Molarity is the amount of solute in moles per liter of solution, written mol/L or M. The IUPAC Green Book calls this quantity amount concentration and lists mol L⁻¹, mmol L⁻¹ and µmol L⁻¹, often written M, mM and µM, as the common units. The letters in front of M are ordinary SI prefixes. NIST lists milli as 10⁻³, micro as 10⁻⁶, nano as 10⁻⁹ and pico as 10⁻¹². So the rules are:
- mM → M: divide by 1,000. 5 mM = 0.005 M.
- M → mM: multiply by 1,000. 0.2 M = 200 mM.
- mM → µM: multiply by 1,000. 2.5 mM = 2,500 µM.
- µM → nM: multiply by 1,000. 0.4 µM = 400 nM.
- nM → µM: divide by 1,000. 750 nM = 0.75 µM.
Every step between neighbouring units is a factor of 1,000. Moving to a smaller unit makes the number larger; moving to a larger unit makes it smaller. If you are two steps apart, such as M to µM, the factor is 1,000 × 1,000 = 1,000,000.
Worked examples: 10 millimolar and 1 millimolar
10 millimolar is 10 × 10⁻³ mol/L = 0.01 M. In smaller units it is 10,000 µM or 10,000,000 nM. If you have 250 mL of a 10 mM solution, it holds 0.01 mol/L × 0.25 L = 0.0025 mol, or 2.5 mmol, of solute. 1 millimolar is 0.001 M, 1,000 µM and 1,000,000 nM. Going the other way, a drug listed at 50 nM is 0.05 µM, 0.00005 mM and 5 × 10⁻⁸ M. Writing the value in scientific notation is the safest way to check: 50 nM = 50 × 10⁻⁹ M = 5 × 10⁻⁸ M.
mM to M conversion table
| mM | M | µM | nM |
|---|---|---|---|
| 0.001 mM | 0.000001 | 1 | 1,000 |
| 0.01 mM | 0.00001 | 10 | 10,000 |
| 0.1 mM | 0.0001 | 100 | 100,000 |
| 0.5 mM | 0.0005 | 500 | 500,000 |
| 1 mM | 0.001 | 1,000 | 1,000,000 |
| 2 mM | 0.002 | 2,000 | 2,000,000 |
| 2.5 mM | 0.0025 | 2,500 | 2,500,000 |
| 5 mM | 0.005 | 5,000 | 5,000,000 |
| 10 mM | 0.01 | 10,000 | 10,000,000 |
| 20 mM | 0.02 | 20,000 | 20,000,000 |
| 25 mM | 0.025 | 25,000 | 25,000,000 |
| 50 mM | 0.05 | 50,000 | 50,000,000 |
| 100 mM | 0.1 | 100,000 | 100,000,000 |
| 150 mM | 0.15 | 150,000 | 150,000,000 |
| 200 mM | 0.2 | 200,000 | 200,000,000 |
| 250 mM | 0.25 | 250,000 | 250,000,000 |
| 500 mM | 0.5 | 500,000 | 500,000,000 |
| 1,000 mM | 1 | 1,000,000 | 1,000,000,000 |
Full molarity conversion chart
Read across: one unit of the row equals the number shown in each column.
| 1 of… | M | mM | µM | nM | pM |
|---|---|---|---|---|---|
| 1 M | 1 | 1,000 | 1,000,000 | 1,000,000,000 | 1,000,000,000,000 |
| 1 mM | 0.001 | 1 | 1,000 | 1,000,000 | 1,000,000,000 |
| 1 µM | 0.000001 | 0.001 | 1 | 1,000 | 1,000,000 |
| 1 nM | 1 × 10⁻⁹ | 0.000001 | 0.001 | 1 | 1,000 |
| 1 pM | 1 × 10⁻¹² | 1 × 10⁻⁹ | 0.000001 | 0.001 | 1 |
mg/mL to molarity (and back)
A mass concentration tells you grams per liter; molarity tells you moles per liter. The bridge between them is the molar mass in g/mol. Because 1 mg/mL is 1 g/L, the formulas are short:
- Molarity (M) = mass concentration (g/L or mg/mL) ÷ molar mass (g/mol)
- Mass concentration (g/L or mg/mL) = molarity (M) × molar mass (g/mol)
- µg/mL is the same as mg/L, and ng/mL is the same as µg/L, so µg/mL ÷ g/mol gives mM.
Example: glucose has a molar mass of 180.16 g/mol (PubChem). A 1 mg/mL solution is 1 g/L ÷ 180.16 = 0.00555 M, or 5.55 mM. Percent weight-by-volume works the same way once you remember that OpenStax defines % w/v as grams per 100 mL: physiological saline at 0.9% w/v contains 9 g NaCl per liter, and 9 ÷ 58.44 = 0.154 M, about 154 mM.
Use the molar mass of the exact form you weigh. A hydrate, a salt form or a free base can have a noticeably different molar mass from the parent compound, so use the molar mass (sometimes printed as formula weight) given for the exact product you weigh.
| Substance | Molar mass (g/mol) | 1 M = g/L | 1 mg/mL = mM | Note |
|---|---|---|---|---|
| Sodium chloride (NaCl) | 58.44 | 58.44 | 17.11 | 0.9% w/v saline = 9 g/L |
| Glucose | 180.16 | 180.16 | 5.55 | 1 mg/mL |
| Tris base | 121.14 | 121.14 | 8.25 | 1 M stock |
| Hydrochloric acid (HCl) | 36.46 | 36.46 | 27.43 | 1 N = 1 M |
| Sodium hydroxide (NaOH) | 39.997 | 39.997 | 25.00 | 1 N = 1 M |
| Sulfuric acid (H₂SO₄) | 98.08 | 98.08 | 10.20 | 1 M = 2 N |
Normality to molarity
Normality (N) counts equivalents per liter instead of moles. An equivalent is the amount that supplies or reacts with one mole of H⁺ in an acid–base reaction, or one mole of electrons in a redox reaction. Weber State University's chemistry notes put it simply: normality is always a multiple of molarity. The multiple is the number of equivalents per mole, n:
- N = M × n and M = N ÷ n
- HCl gives one H⁺, so n = 1 and 1 M = 1 N.
- H₂SO₄ gives two H⁺, so n = 2 and 1 M = 2 N; a 1 N solution is 0.5 M.
- Ca(OH)₂ supplies two OH⁻, so 0.2 M is 0.4 N with respect to OH⁻.
The catch is that n depends on the reaction, not only on the compound. The same notes show copper accepting one electron in one redox reaction and two in another, which changes its equivalent weight. So a normality figure only means something alongside the reaction it refers to, while a molarity has one value for a given solution. Use normality when a procedure or titration protocol specifies it, and enter the equivalents that apply to that reaction.
Capital M, small m and other symbol traps
The symbols look alike but mean very different things. M is molar (mol/L). mM is millimolar. mm is a millimeter, a length; if that is what you need, use the mm to inches converter. A lowercase m on its own is sometimes used for molal (moles per kilogram of solvent), but the IUPAC Green Book warns that it must not be treated as a unit symbol. The Green Book also discourages the word molarity itself, preferring amount concentration, because it is easily confused with molality.
Common mistakes
- Moving the decimal the wrong way. Smaller unit, bigger number: 0.5 M is 500 mM, never 0.0005 mM.
- Counting only one step. M to µM is two steps, a factor of one million.
- Using the wrong molar mass. Check hydrates and salt forms before converting mg/mL to molar.
- Treating mg/mL as mg/L. They differ by 1,000. mg/mL equals g/L.
- Assuming N equals M. Only when one equivalent per mole applies.
Changing units does not change the solution. To make a weaker solution from a stock, use the dilution calculator (C₁V₁ = C₂V₂), which also works out mass to weigh for a target molarity. For temperatures in a protocol, see Celsius to Fahrenheit.
Frequently asked questions
How do I convert mM to molar?
Divide millimolar by 1,000. 10 mM ÷ 1,000 = 0.01 M, and 250 mM = 0.25 M. Milli is the SI prefix for 10⁻³, so one millimolar is one-thousandth of a mole per liter.
How do I convert molar to mM?
Multiply molar by 1,000. 0.5 M × 1,000 = 500 mM, and 1.5 M = 1,500 mM.
What is 10 millimolar in molar?
10 mM is 0.01 M, which is 0.01 mol of solute per liter of solution. It is also 10,000 µM or 10,000,000 nM.
How many micromolar are in 1 millimolar?
1 mM equals 1,000 µM. Milli is 10⁻³ and micro is 10⁻⁶, so each step down the prefix ladder multiplies the number by 1,000.
How many nanomolar are in 1 micromolar?
1 µM equals 1,000 nM. To go from nanomolar to micromolar, divide by 1,000: 250 nM = 0.25 µM.
How do I convert mg/mL to molarity?
Divide the mass concentration in g/L by the molar mass in g/mol. Because 1 mg/mL equals 1 g/L, molarity (M) = (mg/mL) ÷ molar mass. For glucose at 180.16 g/mol, 1 mg/mL is 0.00555 M, or 5.55 mM.
How do I convert molarity to mg/mL?
Multiply the molarity by the molar mass: mg/mL = M × g/mol. A 0.1 M NaCl solution is 0.1 × 58.44 = 5.844 g/L, which is 5.844 mg/mL.
How do I convert normality to molarity?
Divide normality by the number of equivalents per mole: M = N ÷ n. For sulfuric acid in an acid–base reaction, n = 2, so 1 N H₂SO₄ is 0.5 M. For HCl, n = 1 and N equals M.
What is 0.9% saline in mM?
0.9% w/v means 0.9 g per 100 mL, or 9 g/L. Divided by NaCl's 58.44 g/mol that is 154 mM (0.154 M).
Does mM mean millimeter?
No. In a concentration, mM means millimolar (10⁻³ mol/L). The length unit millimeter is written mm, with two lowercase letters. The capital M matters.
Is molarity the same as molality?
No. Molarity (amount concentration) is moles per liter of solution. Molality is moles per kilogram of solvent. The IUPAC Green Book recommends the name amount concentration partly because molarity is easily confused with molality.
Sources & method
- NIST — Metric (SI) prefixes: milli 10⁻³, micro 10⁻⁶, nano 10⁻⁹, pico 10⁻¹²
- IUPAC Green Book, Quantities, Units and Symbols in Physical Chemistry, 3rd ed., §2.10 p. 48 — amount concentration, mol L⁻¹ written M, mM, µM
- IUPAC Gold Book — amount concentration (DOI 10.1351/goldbook.A00295)
- BIPM SI Brochure (9th ed.) — amount concentration and SI prefixes
- OpenStax Chemistry 2e §3.3 (molarity) and §3.4 (mass-volume percent, 0.9% w/v saline)
- Weber State University, Chem 2990 — Molarity and Normality (equivalents, H₂SO₄ and Ca(OH)₂ examples)
- PubChem (NIH) — molecular weights: NaCl 58.44, glucose 180.16, Tris 121.14, HCl 36.46, NaOH 39.997, H₂SO₄ 98.08 g/mol
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