Going from grams to moles for silicon dioxide means dividing by its molar mass, 60.083 g/mol. One gram is 0.0166436 mol, or 16.6436 mmol; 100 mg is 1.6644 mmol; and a 60.083 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, SiO2, which is where these figures come from.
The figure comes from the formula. Silicon dioxide is 28.085 (Si) + 2 × 15.999 (O), which is 60.083 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 2 of the 3 atoms in a formula unit are oxygen, and they account for 31.998 g of the 60.083 g, or 53.26% 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 0.1664 mmol of silicon dioxide; on a three-decimal balance it is 1 mg, or 16.64 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.
Sand, quartz and glass. Also the anti-caking agent in powdered food, where it appears as silica. At 60.083 g/mol it is heavier than 1 of the 8 oxides covered here, and that ranking matters more than it looks: calcium oxide has a molar mass of 56.077 g/mol, so a gram of it contains 7.14% more formula units than a gram of silicon dioxide. Weigh by mass and you are not weighing equal amounts of substance.
Two practical things move the result. Purity below 100% means the weighed mass overstates how much compound you have — at 98% assay, 1.2017 g of every 60.083 g is not the compound — and any water picked up from the air does the same. Both are systematic, so they shift every solution made from that jar in the same direction.
The formula
m- The mass you weighed, in grams
60.083- The molar mass of silicon dioxide 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 60.083 g/mol, the molar mass of silicon dioxide.
- 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 silicon dioxide in moles
0.25 ÷ 60.083 = 0.00416091 mol, or 4.1609 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 16.64 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
2 g of silicon dioxide in moles
2 ÷ 60.083 = 0.0332873 mol, or 33.287 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 16.64 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
25 g of silicon dioxide in moles
25 ÷ 60.083 = 0.416091 mol, or 416.09 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 16.64 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 silicon dioxide (SiO2)?
It is 60.083 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 28.085 (Si) + 2 × 15.999 (O). One mole of silicon dioxide therefore weighs 60.083 g, and a gram of it is 16.644 mmol.
What percentage of silicon dioxide is oxygen?
53.26% by mass. Each formula unit contains 2 oxygen atoms contributing 31.998 g of the 60.083 g total, so 100 g of silicon dioxide contains 53.26 g of oxygen and a kilogram contains 532.56 g of it.
How do I convert grams of silicon dioxide to moles?
Divide the mass in grams by 60.083 g/mol. So 1 g is 0.0166436 mol, 10 g is 0.166436 mol and 100 g is 1.66436 mol. Nothing else enters the calculation — no volume, no temperature, no concentration.
How many moles is 100 g of silicon dioxide?
1.66436 mol, which is 1664.36 mmol. Read the other way, one mole of silicon dioxide is 60.083 g, so 100 g is 1.664 of a mole.
What about milligrams and micromoles?
The same division, scaled. A milligram of silicon dioxide is 16.644 µmol, 10 mg is 166.44 µmol and 100 mg is 1.6644 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 silicon dioxide, which is 0.0163108 mol rather than 0.0166436 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 silicon dioxide
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 2 | 15.999 | 31.998 | 53.26% |
| Silicon (Si) | 1 | 28.085 | 28.085 | 46.74% |
| Total — one mole of silicon dioxide | 60.083 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 60.083 g/mol.
| On the balance | Moles | Millimoles | Micromoles |
|---|---|---|---|
| 1 mg | 0.000017 | 0.0166436 | 16.6436 |
| 5 mg | 0.000083 | 0.0832182 | 83.2182 |
| 10 mg | 0.000166436 | 0.166436 | 166.436 |
| 25 mg | 0.000416091 | 0.416091 | 416.091 |
| 50 mg | 0.000832182 | 0.832182 | 832.182 |
| 100 mg | 0.00166436 | 1.66436 | 1664.36 |
| 250 mg | 0.00416091 | 4.16091 | 4160.91 |
| 500 mg | 0.00832182 | 8.32182 | 8321.82 |
| 1 g | 0.0166436 | 16.6436 | 16,643.6 |
| 2 g | 0.0332873 | 33.2873 | 33,287.3 |
| 5 g | 0.0832182 | 83.2182 | 83,218.2 |
| 10 g | 0.166436 | 166.436 | 166,436 |
| 25 g | 0.416091 | 416.091 | 416,091 |
| 50 g | 0.832182 | 832.182 | 832,182 |
| 100 g | 1.66436 | 1664.36 | 1664364.296057 |
| 250 g | 4.16091 | 4160.91 | 4160910.740143 |
| 500 g | 8.32182 | 8321.82 | 8321821.480286 |
Every row is the mass divided by 60.083 g/mol. A balance reading to 1 mg resolves 16.64 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 |
|---|---|---|---|
| Calcium oxide | CaO | 56.077 | 17.833 |
| Silicon dioxide (this page) | SiO2 | 60.083 | 16.644 |
| Copper(II) oxide | CuO | 79.545 | 12.572 |
| Titanium dioxide | TiO2 | 79.865 | 12.521 |
| Zinc oxide | ZnO | 81.379 | 12.288 |
| Manganese dioxide | MnO2 | 86.93604 | 11.503 |
| Aluminium oxide | Al2O3 | 101.9601 | 9.8078 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.