Density-to-Molarity Converter

Result

Introduction

Molarity (mol/L) can be derived from a solution’s composition and density. In % w/w, the percentage expresses grams of solute per 100 grams of total solution. Converting that to molarity requires density so we can determine how many grams are present in one liter of solution. In contrast, % w/v specifies grams per 100 mL directly, so density is not required. For concentrated or non-aqueous systems, density strongly affects grams per liter and may vary with temperature and formulation.

A third pathway converts molality (mol/kg solvent) to molarity using density and molecular weight, accounting for the mass of solute occupying each liter of solution. This avoids common pitfalls when switching between mass-based and volume-based concentration systems. The calculator normalizes units automatically, shows grams of solute per liter alongside the final molarity, and lets you increase precision when more detail is needed. Warnings appear if entries look physically unlikely, but you can still model nonstandard mixtures.

How to use

1. Pick % w/w, % w/v, or Molality mode.
2. Enter values with units and provide molecular weight. For % w/w and molality, also enter density.
3. Choose 3 or 6 significant figures and select Calculate.
4. Read M (mol/L) and supporting values (grams per liter, mass per liter, fractions).
5. Download a text summary or a one-page PDF for your notes.

Formula notes

% w/w: w=%/100; mass_solution_per_L = ρ·1000 (g); mass_solute_per_L = w·mass_solution_per_L; M = (mass_solute_per_L/MW).
% w/v: M = (10·%w/v)/MW.
Molality: with ρ in kg/L, M = (m·ρ)/(1 + m·MW/1000).   Conversions used: mL→L = ÷1000, g→kg = ÷1000 where applicable.

Disclaimer. Educational use only. Not a substitute for professional judgment.