Moles ↔ Grams Converter

Convert between moles and grams using the molar mass of any compound.

How It Works

Enter a compound formula and either a moles value or a grams value. The calculator looks up the atomic masses of each element from the periodic table, computes the compound's molar mass, then converts in both directions instantly. Changing either field updates the other automatically.

Formula

grams = moles × molar mass | moles = grams ÷ molar mass

Step-by-Step Example: Converting Moles of H₂O to Grams

  1. Find the molar mass of H₂O: (2 × 1.008) + 15.999 = 18.015 g/mol
  2. Multiply: 2 mol × 18.015 g/mol = 36.030 g

Step-by-Step Example: Converting Grams of NaCl to Moles

  1. Find the molar mass of NaCl: 22.990 + 35.453 = 58.443 g/mol
  2. Divide: 117 g ÷ 58.443 g/mol = 2.002 mol

Common Compound Reference Table

H₂O = 18.015 g/mol | NaCl = 58.443 g/mol | CO₂ = 44.010 g/mol | C₆H₁₂O₆ (glucose) = 180.156 g/mol | H₂SO₄ = 98.079 g/mol | NH₃ = 17.031 g/mol | CaCO₃ = 100.087 g/mol

Why Moles-to-Grams Conversion Matters

In laboratory chemistry, reagents are weighed on a balance in grams, but chemical equations are written in molar ratios. Converting between the two is the essential bridge that lets you measure precisely what you need. Whether you are preparing a buffer solution, running a titration, or scaling up a synthesis reaction, this conversion is one of the most common calculations in chemistry.

Significant Figures

The precision of your result should match the precision of your least precise measurement. If you measure 3.0 moles (2 sig figs) of a substance, report the mass to 2 significant figures as well. The calculator shows 4–6 decimal places by default; round appropriately for your lab report or calculation.

Frequently Asked Questions

How do you convert moles to grams?

Multiply the number of moles by the molar mass (g/mol). For example, 3 moles of H₂O: 3 × 18.015 = 54.045 g.

How do you convert grams to moles?

Divide the mass in grams by the molar mass. For example, 36 g of H₂O: 36 ÷ 18.015 = 1.999 mol.

What is a mole in chemistry?

A mole is the SI unit for amount of substance, equal to exactly 6.02214076 × 10²³ elementary entities (Avogadro's number). One mole of any substance has a mass in grams equal to its molar mass.

What is molar mass and how do I find it?

Molar mass is the mass of one mole of a substance, expressed in grams per mole. You find it by summing the atomic masses of all atoms in the chemical formula. For example, H₂SO₄ has 2 H + 1 S + 4 O = 2(1.008) + 32.065 + 4(15.999) = 98.079 g/mol.

Can I use this for molecules with many atoms?

Yes. Enter the molecular formula such as C₆H₁₂O₆ for glucose or C₁₂H₂₂O₁₁ for sucrose, and the calculator will parse each element symbol and subscript correctly.

Why does my result differ slightly from a textbook value?

This calculator uses IUPAC 2021 atomic weights. Some textbooks use older or rounded values (e.g., O = 16 instead of 15.999). For precise work, always cite your source for atomic masses.