Percentage strength for hydrogen peroxide is read as % w/v: grams of solute in 100 mL of solution. So 1% is 1 g per 100 mL, which for this compound works out at 0.294 mol/L, and 0.9% is 9 g per litre or 0.2646 mol/L. The calculator takes a percentage and a volume and returns the grams to weigh, with the molarity and mg/mL equivalents beside it.
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.
Three different percentages are in circulation and they are not interchangeable. Per cent w/v is mass in a volume, the one used here and on medical labels; per cent w/w is mass in mass, the one on drums of concentrated reagent; per cent v/v is volume in volume, used for liquids mixed into liquids. For a dilute aqueous solution w/v and w/w are within a percent of each other, but for anything concentrated the density has to come into it.
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
p- The strength you want, as % w/v
V- The volume of solution, in millilitres
m- The mass of hydrogen peroxide to weigh out, in grams
34.014- The molar mass of hydrogen peroxide in g/mol, derived from its formula
How it works, step by step
- Enter the percentage strength you want, as % w/v.
- Enter the volume of solution in millilitres.
- Grams needed is percentage × volume ÷ 100, since 1% w/v is 1 g per 100 mL.
- The molarity that strength corresponds to for hydrogen peroxide is shown beneath, using 34.014 g/mol.
Worked examples
0.9% w/v hydrogen peroxide in 500 mL
0.9% w/v is 0.9 g per 100 mL, so 500 mL needs 4.5 g. In molar terms that solution is 0.2646 mol/L, and it is 9 mg/mL if you are dosing by volume.
5% w/v hydrogen peroxide in 100 mL
5% w/v is 5 g per 100 mL, so 100 mL needs 5 g. In molar terms that solution is 1.47 mol/L, and it is 50 mg/mL if you are dosing by volume.
10% w/v hydrogen peroxide in 1000 mL
10% w/v is 10 g per 100 mL, so 1000 mL needs 100 g. In molar terms that solution is 2.94 mol/L, and it is 100 mg/mL if you are dosing by volume.
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 many grams of hydrogen peroxide make a 1% w/v solution?
1 g in 100 mL of solution, 5 g in 500 mL, 10 g in a litre. The percentage is fixed to the volume, not to the compound, so those masses are the same whatever is being dissolved — what changes with the compound is the molarity they come to.
What molarity is a 1% w/v solution of hydrogen peroxide?
0.293997 mol/L, because 1% w/v is 10 g/L and 34.014 g/L is one molar. A 0.9% solution is 0.2646 mol/L and a 5% solution is 1.47 mol/L.
Is % w/v the same as % w/w?
No. Per cent w/v is grams per 100 mL of solution; per cent w/w is grams per 100 g of solution. They coincide only when the solution has a density of 1.00 g/mL, which dilute aqueous solutions approximately do and concentrated ones do not. Labels on concentrated reagents are usually w/w.
What is 1% w/v in mg/mL?
10 mg/mL, since 1 g in 100 mL is 1000 mg in 100 mL. For hydrogen peroxide that is also 294 mmol/L, which is the form a dose calculation usually wants.
Percentage strengths of 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.
| Strength | per 100 mL | per 500 mL | per 1 L | Molarity (mol/L) |
|---|---|---|---|---|
| 0.1% w/v | 100 mg | 500 mg | 1 g | 0.0294 |
| 0.25% w/v | 250 mg | 1.25 g | 2.5 g | 0.073499 |
| 0.5% w/v | 500 mg | 2.5 g | 5 g | 0.147 |
| 0.9% w/v | 900 mg | 4.5 g | 9 g | 0.2646 |
| 1% w/v | 1 g | 5 g | 10 g | 0.294 |
| 2% w/v | 2 g | 10 g | 20 g | 0.58799 |
| 3% w/v | 3 g | 15 g | 30 g | 0.88199 |
| 5% w/v | 5 g | 25 g | 50 g | 1.47 |
| 10% w/v | 10 g | 50 g | 100 g | 2.94 |
| 20% w/v | 20 g | 100 g | 200 g | 5.8799 |
A 1% w/v solution is 1 g in 100 mL, which for this compound is 0.294 mol/L because 10 g/L divided by 34.014 g/mol gives that figure.
| 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.