To prepare a solution of hydrogen peroxide you need the grams, and grams is molarity × volume in litres × 34.014 g/mol. A litre of 1 M takes 34.014 g; 500 mL of 0.1 M takes 1.7007 g; 250 mL of 0.01 M takes 85.035 mg. Enter the strength you want and the volume you want it in, and the calculator returns the mass to weigh together with the same figure in milligrams and as a percentage strength.
The figure comes from the formula. Hydrogen peroxide is 2 × 1.008 (H) + 2 × 15.999 (O), which is 34.014 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 4 atoms in a formula unit are oxygen, and they account for 31.998 g of the 34.014 g, or 94.07% by mass. The derivation table below breaks the whole molecule down element by element.
Order of operations matters more than precision here. Dissolve the solid in rather less than the final volume, then make up to the mark once it has all gone into solution and come back to room temperature — warm solutions read low when they cool. If the calculated mass is under about 20 mg, prepare ten times the strength and dilute it tenfold by pipette instead, because C₁V₁ = C₂V₂ carries less error than a marginal weighing.
Sold at 3% for first aid, 6% for hair and 35% for industry. It decomposes to water and oxygen, faster when warm or contaminated. At 34.014 g/mol it is heavier than 6 of the 11 gases and small molecules covered here, and that ranking matters more than it looks: oxygen has a molar mass of 31.998 g/mol, so a gram of it contains 6.3% more formula units than a gram of hydrogen peroxide. 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 34.014 g of hydrogen peroxide — 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
c- The molarity you want, in mol/L
V- The volume you want to make, in millilitres
34.014- The molar mass of hydrogen peroxide in g/mol, derived from its formula
m- The mass of hydrogen peroxide to weigh out, in grams
How it works, step by step
- Enter the molarity you want, in mol/L.
- Enter the volume you want to make, in millilitres.
- The two are multiplied together and by 34.014 g/mol.
- The result is the mass to weigh; dissolve it in part of the volume and then make up to the mark.
Worked examples
250 mL of 0.1 M hydrogen peroxide
Weigh 0.85035 g. That is 0.1 M × 0.25 L × 34.014 g/mol, and it comes to 850.35 mg if your balance is set to milligrams. Dissolve in about 175 mL first, then make up to 250 mL.
500 mL of 0.5 M hydrogen peroxide
Weigh 8.5035 g. That is 0.5 M × 0.5 L × 34.014 g/mol, and it comes to 8503.5 mg if your balance is set to milligrams. Dissolve in about 350 mL first, then make up to 500 mL.
1000 mL of 1 M hydrogen peroxide
Weigh 34.014 g. That is 1 M × 1 L × 34.014 g/mol, and it comes to 34,014 mg if your balance is set to milligrams. Dissolve in about 700 mL first, then make up to 1000 mL.
How to read your score
Frequently asked questions
What is the molar mass of hydrogen peroxide (H2O2)?
It is 34.014 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 2 × 1.008 (H) + 2 × 15.999 (O). One mole of hydrogen peroxide therefore weighs 34.014 g, and a gram of it is 29.4 mmol.
What percentage of hydrogen peroxide is oxygen?
94.07% by mass. Each formula unit contains 2 oxygen atoms contributing 31.998 g of the 34.014 g total, so 100 g of hydrogen peroxide contains 94.07 g of oxygen and a kilogram contains 940.73 g of it.
How much hydrogen peroxide do I need for 1 litre of 1 M solution?
34.014 g — the molar mass in grams, which is what a 1 molar solution means. For 1 L of 0.1 M it is 3.4014 g, and for 1 L of 0.01 M it is 0.34014 g.
How much for 100 mL of 0.1 M?
0.34014 g. The volume is a tenth of a litre and the strength a tenth of molar, so the mass is a hundredth of 34.014 g. In milligrams that is 340.14 mg.
Do I dissolve the solid first or make up the volume first?
Dissolve first, in perhaps 70% of the final volume, then make up to the mark. Adding solid to a full flask overshoots the volume and leaves the solution weak, and undissolved solid at the mark means the strength keeps changing as it goes in.
Can I dilute a stock solution instead of weighing?
Yes, and it is more accurate for small amounts. C₁V₁ = C₂V₂: to get 500 mL of 0.01 M from a 0.5 M stock, take 10 mL of stock and make up to 500 mL. Weighing the 170.07 mg that 500 mL of 0.01 M needs directly is the harder of the two.
Solution recipes for hydrogen peroxide
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 2 | 15.999 | 31.998 | 94.07% |
| Hydrogen (H) | 2 | 1.008 | 2.016 | 5.927% |
| Total — one mole of hydrogen peroxide | 34.014 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 34.014 g/mol.
| Target | for 100 mL | for 250 mL | for 500 mL | for 1 L |
|---|---|---|---|---|
| 0.001 M | 3.4014 mg | 8.5035 mg | 17.007 mg | 34.014 mg |
| 0.005 M | 17.007 mg | 42.5175 mg | 85.035 mg | 170.07 mg |
| 0.01 M | 34.014 mg | 85.035 mg | 170.07 mg | 340.14 mg |
| 0.05 M | 170.07 mg | 425.175 mg | 850.35 mg | 1.7007 g |
| 0.1 M | 340.14 mg | 850.35 mg | 1.7007 g | 3.4014 g |
| 0.15 M | 510.21 mg | 1.27553 g | 2.55105 g | 5.1021 g |
| 0.2 M | 680.28 mg | 1.7007 g | 3.4014 g | 6.8028 g |
| 0.25 M | 850.35 mg | 2.12588 g | 4.25175 g | 8.5035 g |
| 0.5 M | 1.7007 g | 4.25175 g | 8.5035 g | 17.007 g |
| 1 M | 3.4014 g | 8.5035 g | 17.007 g | 34.014 g |
| 2 M | 6.8028 g | 17.007 g | 34.014 g | 68.028 g |
Each cell is molarity × volume in litres × 34.014 g/mol. Dissolve the solid first and then make up to the marked volume — adding solid to a full volume overshoots it.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Carbon monoxide | CO | 28.01 | 35.702 |
| Nitrogen | N2 | 28.014 | 35.696 |
| Oxygen | O2 | 31.998 | 31.252 |
| Hydrogen peroxide (this page) | H2O2 | 34.014 | 29.4 |
| Carbon dioxide | CO2 | 44.009 | 22.723 |
| Propane | C3H8 | 44.097 | 22.677 |
| Butane | C4H10 | 58.124 | 17.205 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.