Enter the concentration in mg/mL and the molecular weight in g/mol into the calculator to convert the concentration to millimolar (mM). You can also enter any two of the three values to solve for the missing variable.
| mg/mL to mM | mM to mg/mL |
|---|---|
| 0.05 mg/mL = 0.856 mM | 1 mM = 0.05844 mg/mL |
| 0.1 mg/mL = 1.711 mM | 2 mM = 0.11688 mg/mL |
| 0.25 mg/mL = 4.279 mM | 5 mM = 0.2922 mg/mL |
| 0.5 mg/mL = 8.557 mM | 10 mM = 0.5844 mg/mL |
| 1 mg/mL = 17.114 mM | 20 mM = 1.1688 mg/mL |
| 2 mg/mL = 34.228 mM | 25 mM = 1.461 mg/mL |
| 5 mg/mL = 85.570 mM | 50 mM = 2.922 mg/mL |
| 10 mg/mL = 171.140 mM | 100 mM = 5.844 mg/mL |
| 20 mg/mL = 342.280 mM | 200 mM = 11.688 mg/mL |
| 50 mg/mL = 855.700 mM | 500 mM = 29.22 mg/mL |
| Formulas: mM = (mg/mL x 1000) / MW and mg/mL = (mM x MW) / 1000. | |
| mg/mL to mM | mM to mg/mL |
|---|---|
| 0.05 mg/mL = 0.278 mM | 1 mM = 0.18016 mg/mL |
| 0.1 mg/mL = 0.555 mM | 2 mM = 0.36032 mg/mL |
| 0.25 mg/mL = 1.388 mM | 5 mM = 0.9008 mg/mL |
| 0.5 mg/mL = 2.775 mM | 10 mM = 1.8016 mg/mL |
| 1 mg/mL = 5.550 mM | 20 mM = 3.6032 mg/mL |
| 2 mg/mL = 11.101 mM | 25 mM = 4.504 mg/mL |
| 5 mg/mL = 27.752 mM | 50 mM = 9.008 mg/mL |
| 10 mg/mL = 55.503 mM | 100 mM = 18.016 mg/mL |
| 20 mg/mL = 111.006 mM | 200 mM = 36.032 mg/mL |
| 50 mg/mL = 277.515 mM | 500 mM = 90.08 mg/mL |
| Formulas: mM = (mg/mL x 1000) / MW and mg/mL = (mM x MW) / 1000. | |
| Compound | Formula | MW (g/mol) | 1 mg/mL = |
|---|---|---|---|
| Sodium chloride | NaCl | 58.44 | 17.11 mM |
| Potassium chloride | KCl | 74.55 | 13.41 mM |
| Calcium chloride | CaCl2 | 110.98 | 9.01 mM |
| Tris base | C4H11NO3 | 121.14 | 8.26 mM |
| Glucose | C6H12O6 | 180.16 | 5.55 mM |
| Sucrose | C12H22O11 | 342.30 | 2.92 mM |
| HEPES | C8H18N2O4S | 238.30 | 4.20 mM |
| EDTA (disodium, dihydrate) | C10H14N2Na2O8 | 372.24 | 2.69 mM |
| DMSO | (CH3)2SO | 78.13 | 12.80 mM |
| SDS | C12H25NaO4S | 288.38 | 3.47 mM |
| Urea | CH4N2O | 60.06 | 16.65 mM |
| BSA | Protein | 66,463 | 0.015 mM |
| IgG antibody (typical) | Protein | ~150,000 | 0.0067 mM |
| All values use mM = (1 / MW) x 1000. For proteins, MW in Daltons where 1 Da = 1 g/mol. | |||
- All Unit Converters
- M to mg/mL Calculator
- mM to mg/mL Calculator
- mg/mL to Molarity Calculator
- Molarity Calculator
- Molarity to Moles Calculator
- Weight to Molarity Converter
mg/mL to mM Conversion Formula
The core formula for converting a mass concentration (mg/mL) to a molar concentration (mM) is:
C(mM) = (C(mg/mL) / MW(g/mol)) x 1000
Where C(mM) is the concentration in millimolar, C(mg/mL) is the mass concentration in milligrams per milliliter, and MW is the molecular weight in grams per mole. The factor of 1000 converts from moles per liter (M) to millimoles per liter (mM).
To reverse the calculation, rearrange the formula: mg/mL = (mM x MW) / 1000. This form is useful when a protocol specifies a molar concentration and you need to weigh out a mass of compound.
Why This Conversion Matters in the Lab
Reagent suppliers typically list concentrations in mg/mL because it reflects what was physically weighed and dissolved. Biological assays, on the other hand, report working concentrations in mM (or uM) because cellular responses depend on the number of molecules present, not their mass. Converting between the two is a daily task in any wet lab.
Stock solution preparation is the most common use case. If a protocol calls for a 10 mM working concentration of a compound, you need to know how many milligrams to dissolve per milliliter of solvent. The molecular weight of the compound bridges the gap between mass and moles. For small molecules (MW under ~500 g/mol), a 1 mg/mL solution yields a relatively high mM value. For proteins and large biomolecules (MW in the tens of thousands), the same 1 mg/mL solution corresponds to a very low mM concentration, often in the micromolar range.
Molar Concentration Unit Scale
Molar concentration units span a wide range. Understanding where mM sits in this hierarchy helps prevent unit errors when reading protocols or papers:
| Unit | Symbol | Relative to 1 M | Typical Use |
|---|---|---|---|
| Molar | M | 1 | Stock solutions, strong acids/bases |
| Millimolar | mM | 10^-3 | Buffers, salts, small molecule reagents |
| Micromolar | uM | 10^-6 | Drug compounds, enzyme substrates |
| Nanomolar | nM | 10^-9 | Antibodies, high-affinity ligands |
| Picomolar | pM | 10^-12 | Trace analytes, PCR primers |
Common Conversion Pitfalls
Using Da vs. kDa without adjusting. Protein molecular weights are often listed in kilodaltons (kDa). A 66.5 kDa protein has a MW of 66,500 g/mol. Plugging in 66.5 instead of 66,500 produces a result that is off by a factor of 1,000.
Confusing mg/mL with ug/mL. A concentration listed as 500 ug/mL is 0.5 mg/mL. Forgetting to convert micrograms to milligrams before applying the formula produces a 1,000-fold error in the final mM value.
Ignoring salt or hydrate forms. Many lab chemicals are sold as hydrates (e.g., CaCl2 * 2H2O, MW 147.01) or as sodium/potassium salts. The molecular weight on the bottle label, not the anhydrous MW from a textbook, is the correct value to use in the conversion.
Assuming mg/mL equals mM. These two units are only numerically equal when the molecular weight happens to be exactly 1,000 g/mol. For all other compounds, they differ, sometimes by orders of magnitude.
Worked Example
Problem: You dissolve 5 mg of HEPES buffer (MW = 238.30 g/mol) in 1 mL of water. What is the molar concentration in mM?
Solution: mM = (5 mg/mL / 238.30 g/mol) x 1000 = 20.98 mM.
Reverse check: mg/mL = (20.98 mM x 238.30 g/mol) / 1000 = 5.00 mg/mL. The round-trip confirms the calculation.
