Percentage Concentration to Molarity Calculator

Convert solution mass percent to molarity (mol/L) and molality (mol/kg), or reverse from molarity back to mass percent.

Preset Reagent (optional)

Mass Percent (%)

Solution Density

g/mL

Molar Mass of Solute

g/mol

Preset Reagent (fills density and MW)

Molarity

mol/L

Solution Density

g/mL

Molar Mass of Solute

g/mol

Molarity

—

Mass Percent

—

Molality

—

Concentration

—

🧫 What is Percentage Concentration to Molarity Conversion?

Percentage concentration to molarity conversion is a fundamental calculation in analytical and preparative chemistry. Many concentrated reagents are sold with mass percent on the label (for example, "37% HCl" or "98% H2SO4") along with a density in g/mL, but laboratory procedures typically call for a specific molarity (mol/L). This calculator converts between the two scales using a simple formula.

The mass percent (also called weight percent or % w/w) expresses the grams of solute per 100 g of solution. Molarity (M or mol/L) expresses the moles of solute per litre of solution. Converting between them requires the solution density to link mass and volume, and the solute molar mass to link grams and moles. The core formula is: M = (% × density × 10) / MW, where the factor of 10 combines the 1000 mL/L unit conversion with the 1/100 from the percent definition.

Common use cases include: preparing a dilute acid from a concentrated stock bottle, verifying that a prepared solution matches its label, calculating the mass of reagent needed for a target molarity, and converting between concentration scales when referencing international protocols. The calculator also outputs molality (mol/kg solvent) which is temperature-independent and used for colligative property calculations, and g/L concentration which is useful for dosing and mass flow calculations.

Nine built-in presets cover the most common concentrated stock solutions found in teaching and research laboratories: hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, glacial acetic acid, ammonia solution, hydrofluoric acid, sodium hydroxide, and ethanol. Select a preset to autofill all parameters, then modify any value to explore the effect on molarity.

📐 Formula

M = (% × ρ × 10) ÷ MW

M = molarity (mol/L)

% = mass percent of solute (0 to 100)

ρ = density of solution (g/mL)

MW = molar mass of solute (g/mol)

10 = unit factor: 1000 mL/L ÷ 100 (from percent)

Example: HCl 37%, density 1.19 g/mL, MW 36.461 → M = (37 × 1.19 × 10) / 36.461 = 12.08 mol/L

% = (M × MW) ÷ (ρ × 10)

Rearranged to find mass percent from molarity

Example: M = 18.39, density = 1.84, MW = 98.079 → % = (18.39 × 98.079) / (1.84 × 10) = 98.00 %

m = M ÷ (ρ − M × MW / 1000)

m = molality (mol/kg solvent)

Denominator = kg of solvent per litre of solution

Example: HCl 12.08 mol/L, density 1.19, MW 36.461 → m = 12.08 / (1.19 − 0.440) = 16.11 mol/kg

📖 How to Use This Calculator

Steps

Choose the conversion direction — Select % to Molarity if you have a reagent bottle showing mass percent, or Molarity to % if you know the molar concentration and want the mass fraction.

Enter or select reagent values — For % to M: type the mass percent from the label, the solution density in g/mL (from the label or SDS), and the solute molar mass in g/mol. Or pick a preset for HCl, H2SO4, HNO3, H3PO4, acetic acid, NH3, HF, NaOH, or ethanol to autofill all fields.

Click Calculate — The calculator returns molarity in mol/L as the primary result, along with molality in mol/kg and g/L concentration as secondary outputs.

Use the reverse mode — Switch to Molarity to % mode and enter your known molarity with density and molar mass to recover the mass percent. This verifies a prepared solution or converts a literature value.

💡 Example Calculations

Example 1 — Concentrated HCl (% to Molarity)

HCl 37% by mass, density 1.19 g/mL, MW 36.461 g/mol

Mass percent = 37 %, density = 1.19 g/mL, MW = 36.461 g/mol.

Numerator: 37 × 1.19 × 10 = 440.3 g mol/L normalised.

Molarity = 440.3 / 36.461 = 12.0759 mol/L.

Molality = 12.0759 / (1.19 − 0.4403) = 12.0759 / 0.7497 = 16.1077 mol/kg.

Concentration = 12.0759 × 36.461 = 440.30 g/L.

Molarity = 12.0759 mol/L | Molality = 16.1077 mol/kg | g/L = 440.30

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Example 2 — Concentrated H2SO4 (% to Molarity)

H2SO4 98% by mass, density 1.84 g/mL, MW 98.079 g/mol

Mass percent = 98 %, density = 1.84 g/mL, MW = 98.079 g/mol.

Molarity = (98 × 1.84 × 10) / 98.079 = 1803.2 / 98.079 = 18.3852 mol/L.

Solvent per litre = 1.84 − 18.3852 × 98.079 / 1000 = 1.84 − 1.8032 = 0.0368 kg/L.

Molality = 18.3852 / 0.0368 = 499.60 mol/kg (extremely high because only 2% is water).

Molarity = 18.3852 mol/L | g/L = 1803.20 g/L

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Example 3 — NaOH 50% Solution (% to Molarity)

NaOH 50% by mass, density 1.525 g/mL, MW 39.997 g/mol

Mass percent = 50 %, density = 1.525 g/mL, MW = 39.997 g/mol.

Molarity = (50 × 1.525 × 10) / 39.997 = 762.5 / 39.997 = 19.0639 mol/L.

Solvent per litre = 1.525 − 19.0639 × 39.997 / 1000 = 1.525 − 0.7625 = 0.7625 kg/L.

Molality = 19.0639 / 0.7625 = 25.0019 mol/kg. g/L = 19.0639 × 39.997 = 762.50 g/L.

Molarity = 19.0639 mol/L | Molality = 25.0019 mol/kg | g/L = 762.50

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❓ Frequently Asked Questions

How do you convert mass percent to molarity?+

Use M = (% × ρ × 10) / MW, where % is mass percent (0 to 100), ρ is solution density in g/mL, and MW is solute molar mass in g/mol. For HCl 37% at density 1.19 g/mL: M = (37 × 1.19 × 10) / 36.461 = 12.08 mol/L. The factor 10 = 1000 mL/L ÷ 100 (percent denominator).

Why do I need density to convert percent to molarity?+

Mass percent gives you the fraction of solute by mass, but molarity is defined per volume of solution. Density (g/mL) converts mass to volume: one litre of solution has mass = density × 1000 g. Without density you cannot determine how many moles fit in a litre. Always use the density of the solution (from the bottle label or SDS), not the density of pure solvent.

What is the molarity of 37% hydrochloric acid?+

Concentrated HCl (37% by mass, density 1.19 g/mL) has a molarity of 12.08 mol/L. This is the standard concentrated hydrochloric acid. To prepare 1 M HCl from the concentrated stock, dilute 83 mL of 12.08 M HCl to 1 litre using the dilution formula M1V1 = M2V2: V1 = (1 × 1000) / 12.08 = 82.8 mL.

What is the molarity of concentrated sulfuric acid?+

Concentrated H2SO4 (98% by mass, density 1.84 g/mL, MW 98.079 g/mol) has a molarity of 18.39 mol/L. It also has an extraordinary molality of about 499 mol/kg because only about 2% of the mass is water. Always add acid to water when diluting, never water to acid.

What is the difference between molarity and molality?+

Molarity (mol/L) is moles per litre of solution and changes slightly with temperature because liquid volume is temperature-dependent. Molality (mol/kg) is moles per kilogram of pure solvent and is temperature-independent. For dilute aqueous solutions they are nearly equal. For concentrated solutions such as 50% NaOH (19.06 M, 25.0 m) or 98% H2SO4 (18.39 M, 499 m), they diverge significantly.

How do I convert molarity back to mass percent?+

Use % = (M × MW) / (ρ × 10), where M is molarity in mol/L, MW is molar mass in g/mol, and ρ is density in g/mL. For HCl M = 12.08, MW = 36.461, density = 1.19: % = (12.08 × 36.461) / (1.19 × 10) = 440.2 / 11.9 = 37.0 %. This calculator's Molarity to % mode does this automatically.

What is the molarity of glacial acetic acid?+

Glacial acetic acid (100% CH3COOH, density 1.049 g/mL, MW 60.052 g/mol) has a molarity of (100 × 1.049 × 10) / 60.052 = 17.47 mol/L. To prepare 1 M acetic acid, dilute 57.2 mL of glacial acetic acid to 1 litre with water.

What is the factor 10 in the formula M = (% x density x 10) / MW?+

The 10 comes from combining two unit conversions: 1000 mL per litre divided by 100 (the denominator in percent). Mass percent gives grams of solute per 100 g solution. Multiplying by density converts to g solute per 100 mL. Multiplying by 10 scales to 1000 mL (one litre). Dividing by molar mass converts grams to moles, giving mol/L.

How is molality calculated from molarity and density?+

Molality m = M / (ρ − M × MW / 1000), where ρ is in g/mL and MW is in g/mol. The denominator represents the mass of solvent in kg per litre of solution: total solution mass minus solute mass. For HCl (M=12.08, ρ=1.19, MW=36.461): denominator = 1.19 − 0.440 = 0.750 kg/L, molality = 12.08 / 0.750 = 16.11 mol/kg.

Can I use this calculator for non-aqueous solvents?+

Yes. The formula M = (% × ρ × 10) / MW works for any solvent as long as the density is the density of the actual solution (not pure solvent). Enter the density from the data sheet. The molar mass is always the molar mass of the solute, regardless of solvent.

What is the molarity of 28% ammonia solution?+

Ammonia solution 28% by mass (density 0.90 g/mL, NH3 MW = 17.031 g/mol) has a molarity of (28 × 0.90 × 10) / 17.031 = 252 / 17.031 = 14.80 mol/L. Note: the molar mass used is that of dissolved NH3 (17.031 g/mol), not ammonium hydroxide (35.046 g/mol). Using the correct MW is important for accuracy.

What should I do if I only know volume percent (v/v) instead of mass percent?+

Volume percent (% v/v) requires a different approach. Convert % v/v to % w/w using: % w/w = (% v/v × density of pure solute) / density of solution. Then use this calculator with the % w/w value. Alternatively, for ethanol v/v concentrations in water, standard conversion tables are available in pharmacopoeias.

🔗 Related Calculators

How do you convert mass percent to molarity?

Use the formula M = (% x density x 10) / MW, where % is mass percent, density is in g/mL, and MW is molar mass in g/mol. For example, HCl 37% at density 1.19 g/mL and MW 36.461 gives M = (37 x 1.19 x 10) / 36.461 = 12.08 mol/L.

What is the formula for converting percent concentration to molarity?

M = (% x rho x 10) / MW where M is molarity in mol/L, % is mass percent (0-100), rho is solution density in g/mL, and MW is solute molar mass in g/mol. The factor of 10 combines the per-100 in percent with the per-1000 in molarity.

What is the molarity of 37% HCl?

At standard conditions, 37% HCl has a density of 1.19 g/mL and MW of 36.461 g/mol. Applying M = (37 x 1.19 x 10) / 36.461 gives 12.08 mol/L. This is the standard concentrated hydrochloric acid used in laboratories.

What is the molarity of 98% H2SO4?

Concentrated sulfuric acid (98% by mass, density 1.84 g/mL, MW 98.079 g/mol) has a molarity of (98 x 1.84 x 10) / 98.079 = 18.39 mol/L. This is approximately 18.4 M, the standard concentrated sulfuric acid.

What is the difference between molarity and molality?

Molarity (mol/L) is moles of solute per litre of solution and changes with temperature because volume changes. Molality (mol/kg) is moles of solute per kilogram of solvent and is temperature-independent. For dilute aqueous solutions they are nearly equal. For concentrated solutions such as 98% H2SO4, they differ dramatically.

Why is density needed to convert mass percent to molarity?

Mass percent tells you the fraction of solute by mass but not the volume. Molarity is defined per volume of solution. Density links mass to volume, making the conversion possible. Without density you cannot determine how many moles are in a litre of solution.

What is the molarity of 28% ammonia solution?

Ammonia solution 28% by mass with density 0.90 g/mL and MW of NH3 = 17.031 g/mol gives M = (28 x 0.90 x 10) / 17.031 = 14.80 mol/L. Note: the molar mass used is that of dissolved NH3, not ammonium hydroxide.

How do you convert molarity back to mass percent?

Reverse the formula: % = (M x MW) / (density x 10). If you know the molarity, molar mass, and solution density, you can find the mass percent. This calculator includes a reverse mode for exactly this purpose.

What is the molarity of glacial acetic acid?

Glacial acetic acid (100% CH3COOH) has density 1.049 g/mL and MW 60.052 g/mol. Molarity = (100 x 1.049 x 10) / 60.052 = 17.47 mol/L. This is commonly used to prepare buffer solutions by diluting to the desired pH.

What does the factor 10 represent in the conversion formula?

The factor 10 = 1000 mL/L divided by 100 (the denominator in percent). Mass percent is grams of solute per 100 g solution. Multiplying by density (g/mL) gives g/mL, then by 1000 gives g/L. Dividing by MW (g/mol) gives mol/L. Combining 1000/100 = 10 simplifies the formula.

📌 Quick Tips

💡The density on a reagent bottle is the density of the solution, not pure solvent. Use the value listed on the label or SDS (Safety Data Sheet).

💡Use the presets for common concentrated acids and bases to auto-fill mass percent, density, and molar mass with standard values.

💡Molality (mol/kg solvent) is temperature-independent and preferred for colligative property calculations such as boiling point elevation and freezing point depression.

💡For very concentrated solutions such as 98% H2SO4, molality is extremely high because almost no free solvent remains.

💡The formula M = (% x density x 10) / MW uses the 10 factor because percent is per 100 g and density is per mL, while molarity is per 1000 mL.