Molar MassMolar mass of carbon dioxide (CO2)
The molar mass of carbon dioxide, CO2, is 44.01 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 44.01 grams.
About carbon dioxide
Carbon dioxide is the gas breathed out by animals, used by plants in photosynthesis and given off when fuels burn. It is about one and a half times as heavy as air, so it can be poured and collects in low places. The solid is called dry ice.
The working
The formula CO2 has 1 carbon atom and 2 oxygen atoms, 3 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 | 27.29% |
| Oxygen (O) | 2 | 15.999 | 31.998 | 72.71% |
12.011 + 2 × 15.999 = 44.009 g/mol
With the rounded atomic masses used in many school books (C = 12, O = 16) the answer is 44 g/mol. The difference from 44.01 is too small to matter in most school sums.
Percentage composition
By mass, CO2 is 27.29% carbon and 72.71% oxygen. The largest share comes from oxygen. In a 100 g sample there are 27.3 g of carbon and 72.7 g of oxygen.
Worked examples
Grams to moles. How many moles are in 50 g of CO2? Divide the mass by the molar mass: 50 ÷ 44.01 = 1.136 mol.
Moles to grams. What is the mass of 0.4 mol of CO2? Multiply: 0.4 × 44.01 = 17.6 g.
Counting particles. 50 g contains 1.136 mol × 6.022 × 1023 = 6.842 × 1023 molecules, and 2.053 × 1024 atoms in all.
As a gas. At 0 °C and 1 atmosphere one mole of an ideal gas occupies 22.4 litres, so the density of CO2 is about 44.01 ÷ 22.4 = 1.96 g per litre. Air averages about 29 g/mol, so this gas is heavier than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 4.401 g |
| 0.5 mol | 22 g |
| 1 mol | 44.01 g |
| 2 mol | 88.02 g |
| 5 mol | 220 g |
| Mass | Moles |
|---|---|
| 1 g | 0.02272 mol |
| 10 g | 0.2272 mol |
| 100 g | 2.272 mol |
| 1 kg | 22.72 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of CO2?
The molar mass of carbon dioxide (CO2) is 44.01 g/mol, or 44.009 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of CO2?
100 ÷ 44.01 = 2.272 mol.
What is the mass of one molecule of CO2?
Divide the molar mass by the Avogadro constant: 44.01 ÷ 6.022 × 1023 = 7.308 × 10-23 g.
What is the percentage of oxygen in CO2?
Oxygen makes up 72.71% of the mass of CO2: 2 × 15.999 ÷ 44.009 × 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.