Grams to Moles Calculator

At a glance:A mole (symbol mol) is the SI base unit of 'amount of substance' — 1 mol of any substance contains the same number of elementary entities (about 6.022 × 10²³, Avogadro's constant N_A) as there are atoms in exactly 12 g of carbon-12. But in the lab we weigh in grams, and in chemical equations we count in moles; converting between 'mass' and 'moles' is the most basic step in stoichiometry. The bridge is the molar mass M, defined as the mass of 1 mol of a substance (unit g/mol), numerically equal to its relative molecular mass (for elements, the relative atomic mass) — e.g. water H₂O M = 2×1 + 16 = 18 g/mol, sodium chloride NaCl M = 22.99 + 35.45 ≈ 58.5 g/mol, iron Fe M = 55.85 g/mol. The conversion formula is n = m / M, where n is the amount of substance (mol), m the mass (g) and M the molar mass (g/mol). From it the reverse follows: m = n × M (moles to grams) and M = m / n (molar mass from mass and moles). Using this tool's default: 18 g of water (M = 18) gives n = 18 / 18 = 1 mol; 5.85 g of NaCl (M = 58.5) gives n = 0.1 mol. The essence of the grams↔moles conversion is 'amount of substance' as the counting unit of particles: 1 mol of any substance always contains N_A particles, so converting mass to moles means converting macroscopically weighable mass into 'how many times N_A particles', so the reaction equation (in mole ratios) can be applied. In real chemistry this conversion appears everywhere: pre-lab weighing and mole counting; using the equation to find how much product from how much reactant (n_reactant → n_product by ratio → m_product); concentration conversion (molarity = moles/volume); dilution; gas law; solution-thermochemistry quantity calculation. Using the formula: first, the molar mass M must match the substance and be in g/mol (often looked up from the periodic table or computed from the formula); the relative molecular mass is numerically equal to it. Second, mass m and molar mass M must use the same mass unit system (grams vs g/mol); mixing mg needs conversion. Third, M must be greater than 0 (a real substance has positive mass). Fourth, for compounds with water of crystallisation count it in; for mixtures use the average molar mass. In short, this simple n = m/M is the foundation of all stoichiometric computation — this calculator does it in one step, ideal for Hong Kong DSE Chemistry mass–mole conversions.