Moles Calculator
Convert between grams, moles, and number of particles using molar mass and Avogadro's number — the core mass-to-moles conversion of chemistry.
Cómo usar esta calculadora
- 1Choose whether you know the mass or the number of moles.
- 2Enter that value.
- 3Enter the substance's molar mass (the sum of its atomic masses).
- 4Read the moles or mass, and the number of particles.
Cómo funciona
Moles, mass, and particles
moles = mass ÷ molar mass mass = moles × molar mass particles = moles × 6.022 × 10²³ 1 mole = Avogadro's number of particles
The mole is the chemist's bridge between the world of grams, which can be measured on a balance, and the world of individual atoms and molecules, which are far too numerous to count. One mole is defined as Avogadro's number of particles — approximately 6.022 × 10²³ — and one mole of any substance has a mass in grams equal to its molar mass, the sum of the atomic masses in its formula. This connection lets you convert freely between mass and amount: dividing a mass by the molar mass gives the number of moles, and multiplying moles by the molar mass gives the mass. Multiplying the number of moles by Avogadro's number gives the actual count of particles. These conversions are the foundational bookkeeping of chemistry, because chemical reactions happen between fixed numbers of particles, so knowing the moles of each substance is what lets a chemist predict how much of one reactant is needed for another and how much product will form.
Ejemplo resuelto
Water has a molar mass of about 18.015 grams per mole (two hydrogen atoms at roughly 1.008 plus one oxygen at 15.999). So 18.015 grams of water is exactly 1 mole, containing about 6.022 × 10²³ water molecules — the same number of molecules as there are in a mole of any other substance.
Moles Calculator: la guía completa
Why chemists count in moles
Chemistry faces a fundamental problem of scale: reactions happen between individual atoms and molecules, which are unimaginably small and numerous, yet chemists work with quantities they can see and weigh. A single drop of water contains more molecules than there are stars in the observable universe. Counting them directly is impossible, so chemistry needs a bridge between the countable, weighable macroscopic world and the invisible microscopic one. The mole is that bridge, and it is arguably the single most important concept in the entire subject.
The mole works by fixing a specific enormous number — Avogadro's number, about 6.022 × 10²³ — as one 'mole' of particles, chosen so that a mole of any substance weighs its molar mass in grams. This clever choice means a chemist can weigh out a known number of moles simply by weighing grams, without ever counting a single atom. Because reactions consume and produce whole numbers of particles in fixed ratios, working in moles lets chemists reason about those ratios using masses they can actually measure. Every quantitative calculation in chemistry, from the lab bench to industrial production, rests on this mass-to-moles conversion.
Molar mass and Avogadro's number
Two quantities make the mole conversions work, and understanding each clarifies the whole idea. Molar mass is the mass of one mole of a substance, in grams per mole, and it is numerically equal to the substance's formula weight — the sum of the atomic masses of all the atoms in its chemical formula, read from the periodic table. Water, H₂O, has a molar mass of about 18 grams per mole because two hydrogens (about 1 each) plus one oxygen (about 16) sum to 18. This numerical equality between atomic mass units and grams per mole is not a coincidence but the very design of the mole.
Avogadro's number is the count of particles in a mole, about 6.022 × 10²³, and it is a fixed constant of nature-by-definition since the 2019 redefinition of the SI units. Its sheer size is what makes the atomic world tractable: because there are so many particles in even a tiny amount of matter, a weighable sample contains a huge but calculable number of them. Multiplying moles by Avogadro's number converts to actual particle counts, which is occasionally needed directly but more often stands behind the scenes, justifying why the mole ratios in a balanced equation correspond to real ratios of atoms and molecules. Together, molar mass and Avogadro's number turn grams into counts and back.
The mole in reactions and beyond
The real power of the mole appears in stoichiometry — the quantitative analysis of chemical reactions. A balanced chemical equation gives the ratios in which substances react, but those ratios are in particles, or equivalently in moles, not in grams. To work out how many grams of one reactant are needed to react completely with a given mass of another, a chemist converts the known mass to moles, applies the mole ratio from the equation, and converts back to grams. Every calculation of how much reactant to use or how much product to expect flows through moles, which is why the mass-to-moles conversion is drilled into every chemistry student.
Beyond reaction calculations, the mole underpins much of the rest of chemistry. Molarity, the most common measure of solution concentration, is moles of solute per litre. Gas laws relate the moles of a gas to its pressure, volume, and temperature. Reaction yields, limiting reactants, and empirical formulas are all mole-based. The concept even extends into everyday relevance whenever quantities of chemicals matter, from dosing medicines to formulating products to understanding nutrition and metabolism at a molecular level. Mastering the simple conversions between mass, moles, and particles is therefore not a narrow skill but the gateway to quantitative chemistry as a whole, which is why it is one of the first and most essential things a chemistry student learns.
Preguntas frecuentes
How do I convert grams to moles?
Divide the mass in grams by the molar mass in grams per mole: moles = mass ÷ molar mass. 18.015 grams of water (molar mass 18.015 g/mol) is 1 mole. To go back, multiply moles by molar mass to get grams.
What is a mole in chemistry?
A mole is a counting unit equal to Avogadro's number of particles — about 6.022 × 10²³. One mole of any substance weighs its molar mass in grams. It bridges the weighable world of grams and the countable world of atoms and molecules, which is why chemists work in moles.
What is Avogadro's number?
Avogadro's number is 6.02214076 × 10²³, the number of particles in one mole. Since 2019 it's a fixed defined constant. Its huge size is why even a small sample of matter contains a vast but calculable number of atoms or molecules, making the atomic world measurable.
How do I find molar mass?
Add up the atomic masses of all the atoms in the chemical formula, from the periodic table. Water (H₂O) is 2 × 1.008 + 15.999 = 18.015 g/mol. The molar mass in grams per mole equals the substance's formula weight in atomic mass units.