Going from grams to moles for propane means dividing by its molar mass, 44.097 g/mol. One gram is 0.0226773 mol, or 22.6773 mmol; 100 mg is 2.2677 mmol; and a 44.097 g portion is exactly one mole. The division is the whole calculation, but the molar mass has to be the one for the exact formula you have, C3H8, which is where these figures come from.
The figure comes from the formula. Propane is 3 × 12.011 (C) + 8 × 1.008 (H), which is 44.097 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Carbon makes up the largest share of the mass: 3 of the 11 atoms in a formula unit are carbon, and they account for 36.033 g of the 44.097 g, or 81.71% by mass. The derivation table below breaks the whole molecule down element by element.
Balance resolution is the practical limit here. On a two-decimal balance the smallest step is 10 mg, which is 0.2268 mmol of propane; on a three-decimal balance it is 1 mg, or 22.68 µmol. To hit a target within 1% you therefore need to weigh at least a gram on the first and at least 100 mg on the second, and below that a stock solution measured by pipette beats weighing.
Bottled gas. The molar mass is what links a cylinder weight to the energy in it, which is how barbecue and heating cylinders are actually sold. At 44.097 g/mol it is heavier than 8 of the 11 gases and small molecules covered here, and that ranking matters more than it looks: carbon dioxide has a molar mass of 44.009 g/mol, so a gram of it contains 0.2% more formula units than a gram of propane. Weigh by mass and you are not weighing equal amounts of substance.
Because this is a gas, volume is often the easier measure. One mole of any ideal gas occupies 22.414 L at 0 °C and 1 atm and 24.4655 L at 25 °C, so 44.097 g of propane — one mole — fills about 24.47 litres at room temperature. Real gases depart from that by a percent or so, more near their boiling point, but for ordinary work the molar volume is the quickest route from grams to litres.
The formula
m- The mass you weighed, in grams
44.097- The molar mass of propane in g/mol, derived from its formula
n- The amount of substance in moles
How it works, step by step
- Enter the mass you weighed, in grams.
- It is divided by 44.097 g/mol, the molar mass of propane.
- The result is the amount of substance in moles, with millimoles and micromoles beneath it.
- Check it against the table if you want the figure for a standard weighing rather than a typed mass.
Worked examples
0.25 g of propane in moles
0.25 ÷ 44.097 = 0.00566932 mol, or 5.6693 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 22.68 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
2 g of propane in moles
2 ÷ 44.097 = 0.0453546 mol, or 45.355 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 22.68 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
25 g of propane in moles
25 ÷ 44.097 = 0.566932 mol, or 566.93 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 22.68 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
How to read your score
Frequently asked questions
What is the molar mass of propane (C3H8)?
It is 44.097 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 3 × 12.011 (C) + 8 × 1.008 (H). One mole of propane therefore weighs 44.097 g, and a gram of it is 22.677 mmol.
What percentage of propane is carbon?
81.71% by mass. Each formula unit contains 3 carbon atoms contributing 36.033 g of the 44.097 g total, so 100 g of propane contains 81.71 g of carbon and a kilogram contains 817.13 g of it.
How do I convert grams of propane to moles?
Divide the mass in grams by 44.097 g/mol. So 1 g is 0.0226773 mol, 10 g is 0.226773 mol and 100 g is 2.26773 mol. Nothing else enters the calculation — no volume, no temperature, no concentration.
How many moles is 100 g of propane?
2.26773 mol, which is 2267.73 mmol. Read the other way, one mole of propane is 44.097 g, so 100 g is 2.268 of a mole.
What about milligrams and micromoles?
The same division, scaled. A milligram of propane is 22.677 µmol, 10 mg is 226.77 µmol and 100 mg is 2.2677 mmol. Working in µmol per mg avoids the string of leading zeros that mol per g produces at this scale.
Does purity change the number of moles?
Yes, in proportion. A 98% pure sample weighing 1 g contains 0.98 g of propane, which is 0.0222237 mol rather than 0.0226773 mol. The calculator assumes the mass you enter is the compound itself, so divide by the assay figure first if you need the corrected amount.
Grams to moles reference for propane
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 3 | 12.011 | 36.033 | 81.71% |
| Hydrogen (H) | 8 | 1.008 | 8.064 | 18.29% |
| Total — one mole of propane | 44.097 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 44.097 g/mol.
| On the balance | Moles | Millimoles | Micromoles |
|---|---|---|---|
| 1 mg | 0.000023 | 0.0226773 | 22.6773 |
| 5 mg | 0.000113386 | 0.113386 | 113.386 |
| 10 mg | 0.000226773 | 0.226773 | 226.773 |
| 25 mg | 0.000566932 | 0.566932 | 566.932 |
| 50 mg | 0.00113386 | 1.13386 | 1133.86 |
| 100 mg | 0.00226773 | 2.26773 | 2267.73 |
| 250 mg | 0.00566932 | 5.66932 | 5669.32 |
| 500 mg | 0.0113386 | 11.3386 | 11,338.6 |
| 1 g | 0.0226773 | 22.6773 | 22,677.3 |
| 2 g | 0.0453546 | 45.3546 | 45,354.6 |
| 5 g | 0.113386 | 113.386 | 113,386 |
| 10 g | 0.226773 | 226.773 | 226,773 |
| 25 g | 0.566932 | 566.932 | 566,932 |
| 50 g | 1.13386 | 1133.86 | 1133863.981677 |
| 100 g | 2.26773 | 2267.73 | 2267727.963354 |
| 250 g | 5.66932 | 5669.32 | 5669319.908384 |
| 500 g | 11.3386 | 11,338.6 | 11338639.816768 |
Every row is the mass divided by 44.097 g/mol. A balance reading to 1 mg resolves 22.68 µmol of this compound, which is the smallest step the middle columns can really move in.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Nitrogen | N2 | 28.014 | 35.696 |
| Oxygen | O2 | 31.998 | 31.252 |
| Hydrogen peroxide | H2O2 | 34.014 | 29.4 |
| Carbon dioxide | CO2 | 44.009 | 22.723 |
| Propane (this page) | C3H8 | 44.097 | 22.677 |
| Butane | C4H10 | 58.124 | 17.205 |
| Sulfur dioxide | SO2 | 64.058 | 15.611 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.