Use this calculator to convert between millimolar (mM) concentration and milligrams per milliliter (mg/mL). Both units appear frequently in biochemistry, pharmacology, and clinical lab work. The conversion requires the molecular weight of your compound. Enter any three of the four fields below and the calculator solves for the missing value.
| mM to mg/mL | mg/mL to mM |
|---|---|
| 0.1 mM = 0.00584 mg/mL | 0.01 mg/mL = 0.171 mM |
| 0.2 mM = 0.0117 mg/mL | 0.05 mg/mL = 0.856 mM |
| 0.5 mM = 0.0292 mg/mL | 0.1 mg/mL = 1.711 mM |
| 1 mM = 0.0584 mg/mL | 0.25 mg/mL = 4.278 mM |
| 2 mM = 0.1169 mg/mL | 0.5 mg/mL = 8.556 mM |
| 5 mM = 0.2922 mg/mL | 0.5844 mg/mL = 10.00 mM |
| 10 mM = 0.5844 mg/mL | 1 mg/mL = 17.11 mM |
| 25 mM = 1.461 mg/mL | 2 mg/mL = 34.22 mM |
| 50 mM = 2.922 mg/mL | 5 mg/mL = 85.56 mM |
| 75 mM = 4.383 mg/mL | 9 mg/mL = 154.0 mM |
| 100 mM = 5.844 mg/mL | 10 mg/mL = 171.1 mM |
| 154 mM = 9.000 mg/mL | 15 mg/mL = 256.7 mM |
| 200 mM = 11.688 mg/mL | 20 mg/mL = 342.2 mM |
| 250 mM = 14.610 mg/mL | 25 mg/mL = 427.8 mM |
| 300 mM = 17.532 mg/mL | 30 mg/mL = 513.4 mM |
| 500 mM = 29.220 mg/mL | 50 mg/mL = 855.6 mM |
| 1000 mM (1 M) = 58.440 mg/mL | 58.44 mg/mL = 1000 mM (1 M) |
| 2000 mM (2 M) = 116.880 mg/mL | 100 mg/mL = 1711 mM |
| 3000 mM (3 M) = 175.320 mg/mL | 150 mg/mL = 2567 mM |
| 5000 mM (5 M) = 292.200 mg/mL | 200 mg/mL = 3422 mM |
| NaCl MW = 58.44 g/mol. Formulas: mg/mL = (mM x MW) / 1000 and mM = (mg/mL x 1000) / MW. | |
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mM to mg/mL Formula
To convert a millimolar (mM) concentration directly to mg/mL:
mg/mL = mM \times MW \div 1000
Where mM is the concentration in millimoles per liter, MW is the molecular weight of the compound in g/mol (numerically identical to mg/mmol), and 1000 converts from per-liter to per-milliliter.
The calculator above uses a related form that accounts for absolute amounts rather than concentration:
mg/mL = mmol \times MW \div V
Here, mmol is the total amount of substance in millimoles, MW is the molecular weight (mg/mmol or g/mol), and V is the total volume in milliliters. Both formulas are equivalent: if your volume is 1 L (1000 mL), they produce the same result.
Quick-Reference: Common Compound Conversions
The table below lists molecular weights for compounds frequently encountered in lab and clinical settings, along with pre-calculated mg/mL values at 1 mM, 10 mM, and 100 mM.
| Compound | MW (g/mol) | 1 mM | 10 mM | 100 mM |
|---|---|---|---|---|
| NaCl | 58.44 | 0.058 mg/mL | 0.584 mg/mL | 5.844 mg/mL |
| KCl | 74.55 | 0.075 mg/mL | 0.746 mg/mL | 7.455 mg/mL |
| CaCl2 | 110.98 | 0.111 mg/mL | 1.110 mg/mL | 11.098 mg/mL |
| Glucose | 180.16 | 0.180 mg/mL | 1.802 mg/mL | 18.016 mg/mL |
| Sucrose | 342.30 | 0.342 mg/mL | 3.423 mg/mL | 34.230 mg/mL |
| Tris base | 121.14 | 0.121 mg/mL | 1.211 mg/mL | 12.114 mg/mL |
| HEPES | 238.30 | 0.238 mg/mL | 2.383 mg/mL | 23.830 mg/mL |
| EDTA (Na2, dihydrate) | 372.24 | 0.372 mg/mL | 3.722 mg/mL | 37.224 mg/mL |
| Urea | 60.06 | 0.060 mg/mL | 0.601 mg/mL | 6.006 mg/mL |
| DMSO | 78.13 | 0.078 mg/mL | 0.781 mg/mL | 7.813 mg/mL |
| SDS | 288.38 | 0.288 mg/mL | 2.884 mg/mL | 28.838 mg/mL |
| Caffeine | 194.19 | 0.194 mg/mL | 1.942 mg/mL | 19.419 mg/mL |
| Aspirin | 180.16 | 0.180 mg/mL | 1.802 mg/mL | 18.016 mg/mL |
| Ethanol | 46.07 | 0.046 mg/mL | 0.461 mg/mL | 4.607 mg/mL |
| Metformin HCl | 165.63 | 0.166 mg/mL | 1.656 mg/mL | 16.563 mg/mL |
| Values calculated using mg/mL = mM x MW / 1000. For hydrated salts, use the MW of the form you are weighing. | ||||
When to Use mM vs. mg/mL
Millimolar (mM) and milligrams per milliliter (mg/mL) both express concentration, but they encode different information. Choosing the right unit depends on the context of your work.
mM (millimolar) counts molecules. One millimolar of any compound contains 6.022 x 1020 molecules per liter. This makes mM the standard unit for enzyme kinetics (Km, Ki), receptor-ligand binding (IC50, EC50), buffer recipes (50 mM Tris-HCl, 150 mM NaCl), and cell culture media. Reaction stoichiometry depends on molar ratios, so mM allows direct comparison regardless of molecular size.
mg/mL measures mass per volume. This is standard for drug formulation and dosing (injectable solutions labeled 10 mg/mL), clinical laboratory reports (blood glucose, serum protein), quality control specifications, and any setting where material is weighed on a balance. Regulatory agencies like the FDA require drug concentrations in mass-per-volume units because dosing is based on weight, not molecular count.
For large biomolecules like proteins (MW 10,000 to 500,000+ g/mol), mg/mL is almost always preferred because molar concentrations become inconveniently small. A 1 mg/mL solution of bovine serum albumin (MW ~66,500) is only about 0.015 mM. Conversely, small molecules like NaCl appear at high mg/mL values even at moderate mM concentrations: physiological saline (154 mM NaCl) is 9.0 mg/mL.
Common Conversion Pitfalls
mM means mmol/L, not mmol/mL. Millimolar is defined as millimoles per liter. The factor of 1000 in the formula (mg/mL = mM x MW / 1000) accounts for the liter-to-milliliter difference. Omitting it produces a result 1000x too high.
Use the molecular weight of what you actually weigh. Calcium chloride is sold as anhydrous CaCl2 (MW 110.98) and as dihydrate CaCl2·2H2O (MW 147.01). Using the wrong form introduces a 32% error. The same applies to Tris base (121.14) vs. Tris-HCl (157.60) and EDTA free acid (292.24) vs. EDTA disodium dihydrate (372.24). Always check the label on the bottle.
Density matters for neat liquids. For dilute aqueous solutions, the formula works directly. For concentrated solutions of dense liquids (DMSO, glycerol), volume changes upon mixing may cause small deviations from the calculated value. At typical working concentrations below 100 mM, this effect is negligible.
Worked Example: Caffeine Solution
Given: Prepare a 5 mM caffeine stock solution. Caffeine has a molecular weight of 194.19 g/mol.
mg/mL = 5 x 194.19 / 1000 = 0.971 mg/mL
To prepare 50 mL of this solution, weigh 0.971 x 50 = 48.55 mg of caffeine, dissolve in water, and bring the final volume to 50 mL.
Reverse check: Converting 0.971 mg/mL back to mM gives 0.971 x 1000 / 194.19 = 5.0 mM, confirming the calculation.
