Mass Percent Calculator

Calculate mass percent composition of a solution or mixture. Find percent by mass (w/w), mass of solute from percent, or grams needed to prepare a target mass percent solution.

⚖️ Solutions📐 mass% = (m_solute/m_solution) × 100🧪 Chemistry

Mass of solute (g)

Mass of solution (g)

OR enter solute mass and solvent mass separately (solution = solute + solvent)

Solvent mass (g, optional instead of solution mass)

Molar mass (optional, for molarity)

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Mass Percent Calculator	—	mass% = (m_solute/m_solution) × 100	% (w/w)

Step-by-Step Examples

Example 1

NaCl Solution

Dissolve 5.85 g NaCl in 94.15 g water.

m_solution = 5.85 + 94.15 = 100.0 g
mass% = 5.85/100.0 x 100 = 5.85%

✓ 5.85% NaCl solution (w/w)

Example 2

Commercial Bleach

Bottle: 8.25 g NaOCl per 100 g solution.

mass% = 8.25/100 x 100 = 8.25% w/w
This is how household bleach concentration is expressed

✓ 8.25% w/w NaOCl

Example 3

Find Solute Mass

How many grams of glucose in 500 g of 20.0% solution?

m_solute = (20.0/100) x 500 = 100 g glucose

✓ 100 g glucose in 500 g of 20% solution

Real-World Applications

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Beverages

Alcohol content by mass (ABW): different from volume percent (ABV). Breweries use both.

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Seawater

Ocean salinity: ~3.5% (35 g salt per 1000 g seawater). Expressed as parts per thousand.

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Lab Reagents

Many commercial reagents labeled by mass percent: 30% H2O2, 37% HCl, 98% H2SO4.

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Dosage Forms

Topical creams expressed in % w/w: 1% hydrocortisone = 1 g per 100 g cream.

Common Mistakes to Avoid

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Solution = solute + solvent

mass% = m_solute / m_solution. Solution mass = solute mass + solvent mass.

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% w/w vs % w/v

w/w: grams per 100 grams. w/v: grams per 100 mL (common in pharma). They are different! Do not confuse.

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Commercial reagents at very high concentration

37% HCl is very concentrated. Molarity = (37/36.46) x (1190 g/L / 100 g) = 12.1 M.

Frequently Asked Questions

What does % w/w mean? ▾

Grams of solute per 100 grams of solution. 5% NaCl = 5 g NaCl per 100 g solution (not per 100 mL).

What is the difference between % w/w and % w/v? ▾

% w/w: g solute per 100 g solution (not volume). % w/v: g solute per 100 mL solution. For water-based dilute solutions, approximately equal (density ~ 1 g/mL).

How do I convert mass percent to molarity? ▾

M = (mass% / 100) x density x 1000 / M_solute. Need density of solution. For dilute aqueous: density ~ 1.00 g/mL.

What is seawater salinity? ▾

About 35 parts per thousand (ppt) or 3.5% by mass. Main salt is NaCl (~78%), plus MgSO4, MgCl2, CaSO4, etc.

What is proof for alcohol? ▾

Proof = 2 x volume% alcohol. 80 proof = 40% by volume (ABV). ABW (mass %) is slightly less than ABV because ethanol density < water density.

Related Chemistry Calculators

Formula Explorer connections

Interpretation: This relationship converts chemical amount, mass, composition or balanced-equation ratios into a reaction quantity. Assumption: Use a balanced reaction, consistent units and the correct molar mass. Purity, side reactions and limiting reagents can change experimental results.

Molar Mass Calculator →Molar Mass Reference Calculator →Molecular Formula Calculator →Chemistry Formula Explorer →