Molarity Calculator

Enter the values you know and this free molarity calculator solves for the missing variable. It works for any compound: small molecules, salts, acids, proteins, or DNA. Type in molecular weight, mass, volume, or desired concentration, and get your answer instantly.

Calculate Molarity of Any Chemical Solution

Molarity tells you how many moles of solute are dissolved in one liter of solution. It is the standard way to express concentration in chemistry and biochemistry research.

This calculator handles four common tasks:

• Find molarity from mass and volume
• Find mass needed to reach a target molar concentration
• Find volume needed for a given mass and concentration
• Dilute a stock solution to a lower concentration

Pick the calculation you need, enter your known values, and the tool returns the result in the unit you choose (M, mM, µM, or nM).

The Molarity Equation and How This Calculator Uses It

The core formula behind every calculation on this page is:

Molarity (M) = moles of solute / liters of solution

Because moles equal mass divided by molecular weight, you can rewrite it as:

M = mass (g) / (molecular weight (g/mol) × volume (L))

The calculator rearranges this equation automatically depending on which variable you leave blank. You always need at least three of the four values (mass, molecular weight, volume, concentration) to solve for the fourth.

Molar Concentration, Molecular Weight, and Volume in the Formula

Molar concentration (molarity) uses the symbol M. A 1 M solution contains one mole of solute per liter of solution.

Molecular weight (also called formula weight or molar mass) is the sum of the atomic weights of every atom in the compound's formula. It is expressed in g/mol. You can find it on the product label, certificate of analysis (COA), or safety data sheet (SDS). Always use the batch-specific molecular weight when available.

Volume is the total volume of the final solution, not the volume of solvent alone. The calculator accepts liters (L) or milliliters (mL) and converts internally.

Calculate the Concentration of a Solution From Mass and Volume

Use this mode when you already dissolved a known mass of compound into a known volume and need to find the resulting molarity.

Inputs: mass (g or mg), molecular weight (g/mol), volume (L or mL).

Example: You dissolve 2 moles of sodium chloride (NaCl) in 1 liter of water. The molarity of that solution is 2 M. In mass terms, the molecular weight of NaCl is 58.44 g/mol, so 2 mol equals 116.88 g.

If you dissolved 5.84 g of NaCl in 500 mL of solution:

1. Convert mass to moles: 5.84 g / 58.44 g/mol = 0.1 mol
2. Convert volume to liters: 500 mL = 0.5 L
3. Molarity = 0.1 mol / 0.5 L = 0.2 M

The calculator performs these steps for you instantly.

Determine the Mass of a Chemical Compound to Prepare a Solution

This is the most common laboratory question: "How much compound do I weigh out?" Enter the target concentration, the volume you want to prepare, and the molecular weight. The calculator returns the mass of compound required.

Formula rearranged: mass (g) = molarity (mol/L) × volume (L) × molecular weight (g/mol)

Example: What is the mass of compound needed to make 10 mL of a 10 mM stock solution when the molecular weight of the compound is 197.13 g/mol?

1. Convert units: 10 mM = 0.01 mol/L; 10 mL = 0.01 L
2. Mass = 0.01 × 0.01 × 197.13 = 0.01971 g = 19.71 mg

Weigh out 19.71 mg, dissolve it, and adjust to a final volume of 10 mL.

Mass in Grams (g) and Milligrams (mg) for Common Compounds

For higher molecular weight compounds, results are often in milligrams. For concentrated solutions of low-MW reagents, results appear in grams.

Another example: What is the mass needed to make 1 mL of a 10 mM solution for a compound of MW 950 g/mol?

• Mass = 0.01 mol/L × 0.001 L × 950 g/mol = 0.0095 g = 9.5 mg

The calculator toggles between g and mg so you can match your balance's readout.

Calculate the Volume Needed for a Target Molar Concentration

When you have a fixed amount of compound (for instance, the entire contents of a vial), this mode tells you how much solvent to add to reach your desired concentration.

Formula rearranged: volume (L) = mass (g) / (molarity (mol/L) × molecular weight (g/mol))

Example: What is the volume of water needed to dissolve 25 mg of a compound at 1 mM concentration when the MW is 1250 g/mol?

1. Convert: 25 mg = 0.025 g; 1 mM = 0.001 mol/L
2. Volume = 0.025 / (0.001 × 1250) = 0.02 L = 20 mL

Add solvent to dissolve the compound, then adjust to a final volume of 20 mL.

Converting Between L, mL, and Other Volume Units

The calculator accepts and converts common volume units:

• 1 L = 1,000 mL
• 1 mL = 1,000 µL
• 1 µL = 0.001 mL

Enter whichever unit is most convenient. The result updates automatically.

How to Dilute a Stock Solution to a Lower Concentration

Preparing stock solutions at a high concentration saves compound and storage space. When you need a working concentration, you dilute. The dilution equation is:

C₁ × V₁ = C₂ × V₂

• C₁ = concentration of the stock solution
• V₁ = volume of stock you need to pipette
• C₂ = desired final concentration
• V₂ = desired final volume

Example: You have a 10 mM stock solution and need 50 mL of a 0.5 mM working solution.

1. V₁ = (C₂ × V₂) / C₁ = (0.5 × 50) / 10 = 2.5 mL
2. Pipette 2.5 mL of stock into a vessel, then add solvent to reach 50 mL total.

Calculate Molarity After Diluting With Water

If you added a known volume of water (or buffer) to a stock and want to find the new concentration, rearrange the equation:

C₂ = (C₁ × V₁) / V₂

Enter stock concentration, the volume of stock you used, and the total final volume. The calculator returns the diluted molarity.

Prepare a Solution in the Laboratory Step by Step

Following a consistent procedure avoids concentration errors.

1. Look up the molecular weight. Check the product label, COA, or SDS. Use the batch-specific molecular weight of the product when it differs from the theoretical value.
2. Enter values into the calculator. Input molecular weight, target concentration, and target volume to find the mass of compound required.
3. Weigh the compound. Use an analytical balance. Tare the weighing vessel first.
4. Dissolve the compound. Transfer the compound to a volumetric flask or graduated cylinder. Add roughly 80% of the final volume of solvent and mix until the solid is fully dissolved.
5. Adjust to final volume. Add solvent to reach the exact target volume. Mix again.
6. Label the container. Include compound name, concentration, date, and solvent.

Dissolve the Compound and Adjust to Final Volume

Some compounds dissolve slowly. Gentle warming or brief sonication can help. If the compound does not dissolve in water, check the label and MSDS for recommended solvents (DMSO is common for hydrophobic small molecules).

Always add solvent to the solute, not the other way around, especially with concentrated acids like HCl. Bring the solution to the final volume mark after the solute is fully dissolved. This ensures accurate molar concentration.

Calculate Molarity for Protein and DNA Research

Proteins, DNA, RNA, and mRNA are large molecules, so their molar concentrations tend to be in the micromolar (µM) or nanomolar (nM) range. The same molarity equation applies. You just need the correct molecular weight.

• Proteins: Molecular weight is often listed in kDa. Multiply by 1,000 to convert to g/mol. For example, a 50 kDa protein has a molecular weight of 50,000 g/mol.
• DNA oligonucleotides: Use the extinction coefficient or an online tool to calculate MW from the sequence. A rough estimate is ~330 g/mol per nucleotide for single-stranded DNA.
• RNA / mRNA: Similar approach. Average nucleotide MW is ~340 g/mol for single-stranded RNA.

Molecular Weight of a Protein or Molecule in mM and µM

Protein stock solutions are rarely in the millimolar range because the masses required would be impractical. Typical working concentrations for assay kits and biochemistry research are 1 to 100 µM.

Example: You have 1 mg of a 25 kDa protein and want to know the molarity if dissolved in 0.5 mL.

1. MW = 25,000 g/mol
2. Moles = 0.001 g / 25,000 g/mol = 4 × 10⁻⁸ mol
3. Concentration = 4 × 10⁻⁸ / 0.0005 L = 8 × 10⁻⁵ M = 80 µM

The calculator handles these unit conversions so you can work directly in mM or µM.

Common Chemical Solutions and Their Molar Concentration

Below are frequently prepared solutions in chemistry and biochemistry labs. Use these as a quick reference, then plug exact values into the calculator.

Sodium Chloride and Other Reagents Used in Biochemistry

Sodium chloride is one of the most common reagents in pharmaceutical and research labs. The weight of NaCl is 58.44 g/mol. To prepare 1 L of 1 M NaCl, weigh out 58.44 g, dissolve in water, and adjust to 1 L.

For buffers and assay reagents, always confirm the molecular weight matches the specific salt form you have (anhydrous vs. hydrate). A hydrated form has extra water molecules that increase the formula weight. Using the wrong MW is the most common source of concentration error.

Molarity Calculator Limitations for Laboratory Use

This calculator provides estimates for planning and preparing solutions. Keep these limitations in mind:

• Purity matters. If your compound is 95% pure, the effective mass of active substance is lower than what you weigh. Adjust accordingly.
• Temperature and density are not included. Molarity changes slightly with temperature because solution volume changes. For most aqueous solutions at room temperature, this effect is small.
• Solubility limits. The calculator does not check whether the compound actually dissolves at the calculated concentration. Always verify solubility data before preparing a solution.
• Not a substitute for professional guidance. For GMP pharmaceutical work, clinical assays, or regulated applications, follow validated protocols reviewed by qualified personnel. This tool is a planning aid, not a certified instrument.
• Significant figures. Results reflect the precision of your inputs. An analytical balance reading to 0.1 mg and a volumetric flask calibrated to ±0.1 mL yield more reliable concentrations than approximate measurements.

For critical research or synthesis work, confirm your prepared concentration with an independent method (spectrophotometry, titration, or refractive index) whenever possible.