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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Mass Percent & Density Calculator

You can calculate mass percent w/w from masses, convert mass percent to molarity with density and molar mass, and find the solute and solvent masses needed to prepare a solution.

Runs in your browserFree · No sign-up · No watermark
MASS % → MOLARITYRuns in your browser
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How files are handled

At a glance

Works with
MASS % → MOLARITY
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Mass Percent & Density Calculator

Mass percent describes a solution by mass: grams of solute per 100 grams of solution. Because volumetric glassware measures volume, converting mass percent to molarity needs the solution's density, which links the mass of a known volume to its solute content.

This calculator covers the three steps that come up in the lab: mass percent from weighed masses, the density conversion to molarity, and the masses of solute and solvent needed to prepare a target mass-percent solution. It shows the formulas and the working.

What this tool does

The details that matter when you use Mass Percent & Density Calculator for real work.

  • Mass percent from masses

    Enter the solute mass with either the solution mass or the solvent mass and get the w/w percentage, with all three masses in the summary.

  • Mass percent to molarity

    Combine a w/w percentage, the solution density and the solute's formula molar mass to get molarity, grams per liter and the density in g/L and kg/m³.

  • Prepare a solution

    Start from a target mass percent and either a solution mass or a volume plus density to get the solute and solvent masses to weigh.

  • Formula molar mass

    The solute formula is parsed with the shared parser, so NaCl, CuSO4 or a hydrate supplies its molar mass without a separate lookup.

  • Worked steps

    Each mode prints the substituted formula, and the density conversion shows both the g/L and kg/m³ forms.

  • Basis stated clearly

    The tool states that the percentage is w/w, distinguishes solution mass from solvent mass and notes that density must be measured at the relevant temperature.

How to use Mass Percent & Density Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose the calculation

    Pick mass percent from masses, mass percent to molarity, or preparation of a target mass-percent solution.

  2. 02

    Enter the masses

    For mass percent, enter the solute mass and specify whether the second mass is the solution or the solvent.

  3. 03

    Convert to molarity

    For molarity, enter the w/w percentage, the solution density in g/mL and the solute formula to use its molar mass.

  4. 04

    Plan a preparation

    For preparation, enter the target percentage and the solution amount as a mass, or as a volume with its density.

  5. 05

    Check the result and steps

    Read the big result and the step panel, then verify that the density corresponds to the temperature at which the solution is used.

How this tool works

Works with
MASS % → MOLARITY
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Assumes a w/w basis and a density measured at the temperature of interest; it does not convert w/v or v/v percentages.
  • Does not account for solute purity, assay or volume contraction on mixing.
  • Ideal-solution arithmetic only; it does not replace a lab protocol or a measured density for exact work.

Privacy and file handling

Masses, percentages, densities and formulas are processed in your browser tab. Nothing is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Mass Percent & Density Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
How do I calculate mass percent of a solution?
Divide the mass of solute by the mass of the whole solution and multiply by 100. For 10 g of solute in 100 g of solution the mass percent is (10 / 100) × 100 = 10% w/w; if you know the solvent mass instead, add it to the solute mass to get the solution mass.
How do I convert mass percent to molarity?
Use C = (w/w% × ρ × 10) / M, with w/w in percent, density ρ in g/mL and molar mass M in g/mol. A 10.0% w/w NaCl solution with density 1.07 g/mL gives C = (10.0 × 1.07 × 10) / 58.44 = 1.83 mol/L.
Why do I need the density to get molarity from mass percent?
Mass percent is a mass ratio, while molarity is moles per liter of solution. The density converts a known volume of solution into its mass, and the mass percent then gives the mass of solute in that volume, which is converted to moles with the molar mass.
What is the difference between w/w and w/v percentages?
A w/w percentage compares masses (grams of solute per 100 grams of solution), while a w/v percentage compares mass to volume (grams per 100 mL). They are different measures and need different conversions; this calculator works on the w/w basis.
How do I prepare a 10% w/w solution?
Weigh solute equal to 10% of the total solution mass and add solvent to reach the rest. For 250 g of solution, weigh 25 g of solute and add 225 g of solvent; if the target is given by volume, multiply the volume by the density to get the solution mass first.
Does temperature affect the mass percent or the molarity?
Mass percent is unaffected by temperature because both masses are stable, but density changes with temperature, so the same w/w solution has a different molarity at a different temperature. Use a density measured at the temperature where the solution is used.
Can I use the solute formula to get the molar mass automatically?
Yes. The formula parser handles element symbols, subscripts, brackets and hydrates, so entering NaCl, CuSO4 or CuSO4·5H2O supplies the matching molar mass. Unknown symbols and malformed formulas are reported instead of guessed.
Does the calculator account for solute purity or volume contraction?
No. The arithmetic assumes the solute is 100% pure and that the density already reflects the real solution. For an assay value, divide the required mass by the purity fraction, and remember that mixing can change the final volume slightly.

Background reading

Format guides that explain the trade-offs behind Mass Percent & Density Calculator.