Moles to Grams Calculator
Convert any amount in moles to grams using the substance's molecular weight. Ideal for chemistry students and lab technicians preparing solutions or scaling reactions.
About this calculator
The mole is the SI unit for amount of substance, and converting between moles and grams is one of the most fundamental operations in chemistry. The formula is: mass (g) = moles (mol) × molecular weight (g/mol). Molecular weight, also called molar mass, is the mass of one mole of a substance and is found by summing the atomic masses of all atoms in a molecular formula. For example, water (H₂O) has a molar mass of 18.015 g/mol. This conversion is essential for weighing out reactants, calculating theoretical yields, and preparing standard solutions in the lab. The reverse operation (grams to moles) simply divides mass by molecular weight.
How to use
Suppose you need 2.5 moles of sodium chloride (NaCl) for an experiment. NaCl has a molecular weight of 58.44 g/mol (Na: 22.99 + Cl: 35.45). Apply the formula: mass = moles × molecular weight = 2.5 × 58.44 = 146.1 g. Enter 2.5 in the 'Number of moles' field and 58.44 in the 'Molecular weight' field. The calculator instantly returns 146.1 g — that is how much NaCl you need to weigh out on your balance.
Frequently asked questions
How do I find the molecular weight of a compound to use in this calculator?
Molecular weight is calculated by adding up the atomic masses of every atom in the chemical formula, using values from the periodic table. For example, glucose (C₆H₁₂O₆) has a molar mass of (6 × 12.011) + (12 × 1.008) + (6 × 15.999) = 180.156 g/mol. Most chemistry textbooks, online databases like PubChem, and periodic tables list molar masses for common compounds. Make sure to account for every atom and its subscript in the formula.
What is the difference between moles and grams in chemistry?
Grams measure mass — a physical quantity you can read directly off a balance. Moles measure the amount of substance in terms of the number of particles, where one mole equals 6.022 × 10²³ particles (Avogadro's number). Because chemical reactions occur between particles in fixed ratios, chemists work in moles for calculations but must convert to grams to actually weigh things out. The molar mass acts as the conversion factor linking these two units.
When would I need to convert moles to grams in a lab setting?
You convert moles to grams whenever you need to physically measure out a reagent. Stoichiometric calculations tell you how many moles of each substance a reaction requires, but laboratory balances measure in grams. For instance, if a synthesis calls for 0.1 mol of potassium permanganate (KMnO₄, MW = 158.03 g/mol), you calculate 0.1 × 158.03 = 15.8 g and weigh that amount. This conversion is also used when preparing solutions of a known molar concentration.