Molar MassMolar mass of methanol (CH3OH)
The molar mass of methanol, CH3OH, is 32.04 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 32.04 grams.
32.04 g/mol
12.011 + 4 × 1.0080 + 15.999 = 32.042 · 6 atoms in the formula · also called methyl alcohol, wood spirit
About methanol
Methanol is the simplest alcohol. It is poisonous and is used as a solvent, a fuel and a starting material for other chemicals.
Other names: methyl alcohol, wood spirit.
The working
The formula CH3OH has 1 carbon atom, 4 hydrogen atoms and 1 oxygen atom, 6 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Carbon (C) | 1 | 12.011 | 12.011 | 37.49% |
| Hydrogen (H) | 4 | 1.0080 | 4.032 | 12.58% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 49.93% |
12.011 + 4 × 1.0080 + 15.999 = 32.042 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1, O = 16) the answer is 32 g/mol. The difference from 32.04 is too small to matter in most school sums.
Percentage composition
By mass, CH3OH is 37.49% carbon, 12.58% hydrogen and 49.93% oxygen. The largest share comes from oxygen. In a 100 g sample there are 37.5 g of carbon, 12.6 g of hydrogen and 49.9 g of oxygen.
Notice that hydrogen has more atoms in the formula (4) than oxygen (1), yet gives a smaller share of the mass. Percentage by mass depends on how heavy each atom is, not only on how many there are.
Worked examples
Grams to moles. How many moles are in 250 g of CH3OH? Divide the mass by the molar mass: 250 ÷ 32.04 = 7.802 mol.
Moles to grams. What is the mass of 0.2 mol of CH3OH? Multiply: 0.2 × 32.04 = 6.408 g.
Counting particles. 250 g contains 7.802 mol × 6.022 × 1023 = 4.699 × 1024 molecules, and 2.819 × 1025 atoms in all.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 3.204 g |
| 0.5 mol | 16.02 g |
| 1 mol | 32.04 g |
| 2 mol | 64.08 g |
| 5 mol | 160.2 g |
| Mass | Moles |
|---|---|
| 1 g | 0.03121 mol |
| 10 g | 0.3121 mol |
| 100 g | 3.121 mol |
| 1 kg | 31.21 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of CH3OH?
The molar mass of methanol (CH3OH) is 32.04 g/mol, or 32.042 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of CH3OH?
100 ÷ 32.04 = 3.121 mol.
What is the mass of one molecule of CH3OH?
Divide the molar mass by the Avogadro constant: 32.04 ÷ 6.022 × 1023 = 5.321 × 10-23 g.
What is the percentage of oxygen in CH3OH?
Oxygen makes up 49.93% of the mass of CH3OH: 1 × 15.999 ÷ 32.042 × 100.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.