Going from grams to moles for sulfuric acid means dividing by its molar mass, 98.072 g/mol. One gram is 0.0101966 mol, or 10.1966 mmol; 100 mg is 1.0197 mmol; and a 98.072 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, H2SO4, which is where these figures come from.
The figure comes from the formula. Sulfuric acid is 2 × 1.008 (H) + 32.06 (S) + 4 × 15.999 (O), which is 98.072 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: 4 of the 7 atoms in a formula unit are oxygen, and they account for 63.996 g of the 98.072 g, or 65.25% 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 0.102 mmol of sulfuric acid; on a three-decimal balance it is 1 mg, or 10.2 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.
Battery acid and the most produced industrial chemical. Concentrated is 98% w/w, about 18.4 mol/L, and it must be added to water rather than the reverse. At 98.072 g/mol it is heavier than 8 of the 12 acids covered here, and that ranking matters more than it looks: phosphoric acid has a molar mass of 97.99376 g/mol, so a gram of it contains 0.0798% more formula units than a gram of sulfuric acid. Weigh by mass and you are not weighing equal amounts of substance.
One more step applies if you are starting from a concentrated bottle. Concentrated acids are labelled as a percentage by weight together with a density, not as a molarity, so getting to mol/L means multiplying density by that percentage and dividing by 98.072 g/mol. A page like this one gives you the last of those three numbers; the first two are on the bottle, and they vary between grades.
The formula
m- The mass you weighed, in grams
98.072- The molar mass of sulfuric acid 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 98.072 g/mol, the molar mass of sulfuric acid.
- 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 sulfuric acid in moles
0.25 ÷ 98.072 = 0.00254915 mol, or 2.5491 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 10.2 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
2 g of sulfuric acid in moles
2 ÷ 98.072 = 0.0203932 mol, or 20.393 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 10.2 µmol, so quoting the answer to more than four significant figures claims a precision the weighing did not have.
25 g of sulfuric acid in moles
25 ÷ 98.072 = 0.254915 mol, or 254.91 mmol. If the balance was reading to 1 mg, the last digit of that mass is worth 10.2 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 sulfuric acid (H2SO4)?
It is 98.072 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 2 × 1.008 (H) + 32.06 (S) + 4 × 15.999 (O). One mole of sulfuric acid therefore weighs 98.072 g, and a gram of it is 10.197 mmol.
What percentage of sulfuric acid is oxygen?
65.25% by mass. Each formula unit contains 4 oxygen atoms contributing 63.996 g of the 98.072 g total, so 100 g of sulfuric acid contains 65.25 g of oxygen and a kilogram contains 652.54 g of it.
How do I convert grams of sulfuric acid to moles?
Divide the mass in grams by 98.072 g/mol. So 1 g is 0.0101966 mol, 10 g is 0.101966 mol and 100 g is 1.01966 mol. Nothing else enters the calculation — no volume, no temperature, no concentration.
How many moles is 100 g of sulfuric acid?
1.01966 mol, which is 1019.66 mmol. Read the other way, one mole of sulfuric acid is 98.072 g, so 100 g is 1.02 of a mole.
What about milligrams and micromoles?
The same division, scaled. A milligram of sulfuric acid is 10.197 µmol, 10 mg is 101.97 µmol and 100 mg is 1.0197 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 sulfuric acid, which is 0.00999266 mol rather than 0.0101966 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 sulfuric acid
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 4 | 15.999 | 63.996 | 65.25% |
| Sulfur (S) | 1 | 32.06 | 32.06 | 32.69% |
| Hydrogen (H) | 2 | 1.008 | 2.016 | 2.056% |
| Total — one mole of sulfuric acid | 98.072 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 98.072 g/mol.
| On the balance | Moles | Millimoles | Micromoles |
|---|---|---|---|
| 1 mg | 0.000010 | 0.0101966 | 10.1966 |
| 5 mg | 0.000051 | 0.050983 | 50.983 |
| 10 mg | 0.000101966 | 0.101966 | 101.966 |
| 25 mg | 0.000254915 | 0.254915 | 254.915 |
| 50 mg | 0.00050983 | 0.50983 | 509.83 |
| 100 mg | 0.00101966 | 1.01966 | 1019.66 |
| 250 mg | 0.00254915 | 2.54915 | 2549.15 |
| 500 mg | 0.0050983 | 5.0983 | 5098.3 |
| 1 g | 0.0101966 | 10.1966 | 10,196.6 |
| 2 g | 0.0203932 | 20.3932 | 20,393.2 |
| 5 g | 0.050983 | 50.983 | 50,983 |
| 10 g | 0.101966 | 101.966 | 101,966 |
| 25 g | 0.254915 | 254.915 | 254,915 |
| 50 g | 0.50983 | 509.83 | 509,830 |
| 100 g | 1.01966 | 1019.66 | 1019659.026022 |
| 250 g | 2.54915 | 2549.15 | 2549147.565054 |
| 500 g | 5.0983 | 5098.3 | 5098295.130108 |
Every row is the mass divided by 98.072 g/mol. A balance reading to 1 mg resolves 10.2 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 |
|---|---|---|---|
| Oxalic acid | C2H2O4 | 90.034 | 11.107 |
| Lactic acid | C3H6O3 | 90.078 | 11.101 |
| Phosphoric acid | H3PO4 | 97.99376 | 10.205 |
| Sulfuric acid (this page) | H2SO4 | 98.072 | 10.197 |
| Tartaric acid | C4H6O6 | 150.086 | 6.6628 |
| Ascorbic acid | C6H8O6 | 176.124 | 5.6778 |
| Citric acid | C6H8O7 | 192.123 | 5.205 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.