Calculate molarity to mg/mL, find required mass, volume, or dilution values from molecular weight, and convert between concentration units.
Molarity to mg/mL Formula
The converter uses two formulas depending on the active mode.
Concentration mode (molarity to mg/mL):
- mg/mL — concentration in milligrams per milliliter (equivalent to g/L)
- M — molarity in mol/L
- MW — molecular weight in g/mol
Mass-to-weigh mode (how much solid to dissolve):
- M — desired molarity in mol/L
- MW — molecular weight in g/mol
- V — final volume in liters
Both formulas use the measured final solution volume; no ideal-solution or negligible solute-volume assumption is required. For hydrated salts, use the MW of the hydrate, not the anhydrous form. For acids and bases supplied as concentrated stocks, also account for purity and density before weighing.
Reference Values
Common molecular weights for quick lookup:
| Compound | Formula | MW (g/mol) |
|---|---|---|
| Sodium chloride | NaCl | 58.44 |
| Potassium chloride | KCl | 74.55 |
| Tris base | C₄H₁₁NO₃ | 121.14 |
| Sodium hydroxide | NaOH | 40.00 |
| Glucose | C₆H₁₂O₆ | 180.16 |
| Sucrose | C₁₂H₂₂O₁₁ | 342.30 |
| EDTA disodium dihydrate | C₁₀H₁₄N₂Na₂O₈ · 2H₂O | 372.24 |
Unit equivalents you can use to sanity-check a result:
| From | To | Multiply by |
|---|---|---|
| mg/mL | g/L | 1 |
| mg/mL | µg/mL | 1,000 |
| mg/mL | mg/L | 1,000 |
| mM | mol/L | 0.001 |
| µM | mol/L | 0.000001 |
Example
Convert 100 mM NaCl to mg/mL.
- Convert molarity to mol/L: 100 mM = 0.1 mol/L
- Multiply by MW: 0.1 × 58.44 = 5.844 g/L
- Result: 5.844 mg/mL
To prepare 500 mL of this solution, multiply mass by volume in liters: 5.844 g/L × 0.5 L = 2.922 g of NaCl dissolved up to a final volume of 500 mL.
FAQ
Is mg/mL the same as g/L? Yes. They are numerically identical because 1 g/L = 1 mg/mL.
Which MW should I use for a hydrate? Use the molecular weight of the hydrated form listed on the bottle. The water of crystallization adds mass that you are weighing out.
What if my reagent is not 100% pure? Divide the calculated mass by the purity fraction. For 95% pure material, weigh mass / 0.95.
