If you do pick up some food grade it’s best to get the 35% (I like Bulk Peroxide). It’s easy to calculate dilution percentages from there. Or you can use this old school maffs formula. It is best to weigh this out (remember 1ml = 1g). You absolutely MUST wear gloves to handle this stuff. It is very caustic and will eat your skin away. Ask me how I know. Anyway, I use it in the garden mostly, but also for other normal house hold and health reasons.
The dilution calculator equation (calculating in gallons) is:
A = Y x B : X
A: The amount of H2O2 you need to mix with water to dilute
Y: The percentage of hydrogen peroxide that you want to achieve in the final mixture
B: The volume of the final mixture of tap water and diluted hydrogen peroxide that you have to decide beforehand
X: The percentage of the hydrogen peroxide application you are trying to dilute
For example, when you want to dilute 35 hydrogen peroxide to 3, the first step is to decide the final volume of the mixture. If you want to make one gallon (about 3.8 liters) of the mixture, you will need:
3 x 1 : 35 = approximately 0.086 gallon of 35% H2O2
But how to dilute 35 hydrogen peroxide in solution physically? You will need to buy measuring cups to get the exact amount of H2O2 and mix it in a plastic tank with zero metal or chemicals such as iron pipe residue.
After finding out how much H2O2 you need to mix with water, you can find out the volume of water that you need to add by following this dilution equation:
Water = B – A