Molarity Calculator

This professional-grade molarity calculator helps scientists, students, and lab technicians compute solution molarity (M), the required mass of a solute, or the volume of solution needed. It supports unit conversions, inline validation, and clear step-by-step outputs to reduce setup errors at the bench.

Interactive Calculator

Choose calculation mode
Enter the molar mass of the solute in grams per mole (e.g., NaCl = 58.44 g/mol).
Mass of the pure solute to dissolve. Choose units below.
Target molarity of the final solution. Choose units below.
Final total volume of the solution. Choose units below.

Results

Molarity —
Required mass —
Required volume —
Derived units —
Enter values above and press Calculate to see the worked steps here.

Data Source and Methodology

Authoritative source: IUPAC, Compendium of Chemical Terminology (the “Gold Book”), 2nd ed. (1997) — “amount-of-substance concentration (molarity)”. Updated version: 2019. Link: https://goldbook.iupac.org/terms/view/C01222. Supplementary unit standards: BIPM, The International System of Units (SI Brochure), 9th ed. (2019), for liter and mole.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Molarity: \( M = \dfrac{n}{V} \) where \( n \) is moles of solute and \( V \) is solution volume in liters.
Using mass and molecular weight: \( M = \dfrac{m / MW}{V} = \dfrac{m}{MW \cdot V} \)
Rearrangements: \( m = M \cdot MW \cdot V \) and \( V = \dfrac{m}{MW \cdot M} \)
Unit conversions: \( 1\,\text{L} = 1000\,\text{mL} = 10^6\,\mu\text{L};\quad 1\,\text{g} = 1000\,\text{mg} = 10^6\,\mu\text{g} \)

Glossary of Variables

  • Molecular weight (MW): mass per mole of solute, in g/mol.
  • Mass (m): amount of solute in grams (input may be µg, mg, g).
  • Volume (V): final solution volume in liters (input may be µL, mL, L).
  • Molarity (M): concentration in mol/L (display in µM, mM, or M).
  • Derived units: alternate views of the main result to minimize manual conversions.

How It Works: A Step-by-Step Example

Problem: How many grams of NaCl are needed for 250 mL of a 0.5 M solution?

  1. Input MW = 58.44 g/mol (NaCl), target concentration = 0.5 M, volume = 250 mL.
  2. Convert volume to liters: 250 mL = 0.250 L.
  3. Apply formula: \( m = M \cdot MW \cdot V = 0.5 \cdot 58.44 \cdot 0.250 = 7.305 \,\text{g} \).
  4. Convert to mg if desired: 7.305 g = 7305 mg.

Answer: 7.305 g of NaCl (7305 mg).

Frequently Asked Questions (FAQ)

What is molarity (M)?

Molarity is moles of solute per liter of solution (mol/L), per IUPAC definition.

Which modes does this calculator support?

You can compute molarity from mass and volume, required mass from molarity and volume, or required volume from mass and molarity.

How do I choose the correct units?

Select the unit next to each input field. The tool converts everything to base SI internally to avoid mistakes.

Does purity or hydration state matter?

This calculator assumes pure anhydrous solute. If your compound has waters of hydration or known purity, adjust the effective MW or mass accordingly.

How many decimals should I use?

Use enough decimals to reflect your instrument precision. You can set the display rounding; internal math uses full precision.

Can I calculate normality (N)?

No. Normality depends on reaction equivalence and is not covered here. Convert to molarity once you know the equivalence factor.

Why is density not required?

Because molarity is defined using the final volume of solution. Density is relevant for mass or volume conversions of solvents but not needed for M directly.

Strumento sviluppato da Ugo Candido,. Contenuti verificati da,.

Ultima revisione per l'accuratezza in data: September 15, 2025.