Millimolar (mM) Calculator
Quickly convert between concentration, mass, and dilution values for lab prep.
Output: required compound mass in mg and g.
Output: resulting concentration in mM.
Output: stock volume (V1) and diluent volume.
What does millimolar mean?
Millimolar (mM) is a concentration unit used constantly in chemistry, biology, biochemistry, and molecular biology labs. It describes how many millimoles of a substance are present per liter of solution.
- 1 M (molar) = 1 mole per liter
- 1 mM (millimolar) = 0.001 moles per liter
- 1 mM = 1 mmol/L
In practical lab work, mM is convenient because many reagents are used in ranges like 0.1 mM, 5 mM, 50 mM, or 100 mM rather than full molar units.
How this millimolar calculator works
This page includes three useful calculators in one:
- Mass from target mM: how much solid compound to weigh.
- mM from measured mass: what concentration you actually made.
- Dilution calculator: how much stock and diluent to combine using C1V1 = C2V2.
Formula 1: Mass needed from target concentration
mass (mg) = target concentration (mM) × volume (mL) × molecular weight (g/mol) ÷ 1000
This is ideal when preparing fresh buffers, standards, and assay mixes from dry powder.
Formula 2: Concentration from mass and volume
concentration (mM) = mass (mg) × 1000 ÷ [molecular weight (g/mol) × volume (mL)]
Use this when you already weighed material and want to verify final concentration.
Formula 3: Dilution equation
C1 × V1 = C2 × V2
If C1 is stock concentration, C2 is target concentration, and V2 is final volume:
V1 = (C2 × V2) ÷ C1
Then diluent volume = V2 - V1.
Worked examples
Example A: Prepare 10 mM glucose, 50 mL
- Target = 10 mM
- Volume = 50 mL
- Molecular weight (glucose) = 180.16 g/mol
mass = 10 × 50 × 180.16 ÷ 1000 = 90.08 mg
Example B: You dissolved 25 mg compound in 100 mL
- Mass = 25 mg
- Volume = 100 mL
- Molecular weight = 342.30 g/mol
concentration = 25 × 1000 ÷ (342.30 × 100) = 0.730 mM (approximately)
Example C: Make 20 mL of 25 mM from 500 mM stock
- C1 = 500 mM
- C2 = 25 mM
- V2 = 20 mL
V1 = (25 × 20) ÷ 500 = 1.0 mL stock
Diluent = 20 - 1 = 19.0 mL
Common mistakes this tool helps you avoid
- Mixing up mg and g: A 1000x error can happen instantly.
- Using wrong molecular weight: hydrate vs anhydrous forms differ.
- Ignoring final volume: concentration depends on total final volume, not just solvent added early.
- Unit confusion: mM, µM, mg/mL, and g/L are not interchangeable without conversion.
Practical lab tips
- Always record reagent lot, molecular weight source, and date.
- For sensitive assays, use calibrated pipettes and analytical balances.
- When possible, prepare concentrated stock solutions and dilute freshly.
- Label containers with concentration, solvent, and pH.
Final note
A reliable millimolar calculator saves time and reduces avoidable prep errors. Use it as a quick check before making standards, buffers, cell culture supplements, or assay reagents. If your protocol has strict requirements (temperature, density, hydration state, or purity corrections), include those adjustments in your final calculation record.