For general cleaning, the everyday hydrogen peroxide sold in US drugstores is 3%, and it works fine for most surfaces. For disinfecting, the concentration matters less than the contact time, so the practical answer is to use the common 3% solution and leave it wet on the surface for a while.
A few points from the guidance I know of (EPA and CDC materials on hydrogen peroxide as a disinfectant):
- 3% household solution: the usual choice. Used as a disinfectant, it generally needs to stay visibly wet on a hard, nonporous surface for about 1 to 10 minutes, depending on the product and the germ. Check the label of your specific bottle, because disinfecting claims are set by the product's EPA registration.
- 6% to 7.5% solutions: stronger, and used for some disinfecting, but they can bleach fabrics and irritate skin and eyes. Handle with gloves and ventilation.
- Higher concentrations (above 10%): industrial or food-grade products. Not appropriate for household use.
Two cautions: never mix hydrogen peroxide with vinegar or other acids in the same container, since this can form peracetic acid, which is harmful. Also, peroxide loses strength when exposed to light and air, so store it in its original dark bottle and replace it after it has been open for a while.
If you need a disinfectant for a specific situation, such as food contact surfaces, a medical setting, or someone who is immunocompromised, check the EPA's registered-disinfectant list or ask a professional. Has anyone here used peroxide for cleaning surfaces, and how did you handle contact time?
How do you dilute to 3% solution from a 30% ACS grade hydrogen peroxide bottle to use in a 24oz spray bottle?
Use the 1-to-9 rule: 1 part 30% peroxide to 9 parts water gives 3%. For a 24 fl oz spray bottle, that means about 2.4 fl oz (71 mL) of 30% peroxide and 21.6 fl oz (639 mL) of cool water. Add the peroxide to the water, not the other way around, and mix gently. Use a graduated measuring tool, since small measuring errors matter at this strength. The formula is C1 × V1 = C2 × V2: 30% × V1 = 3% × 24 oz, so V1 = 2.4 oz.
30% is a strong oxidizer. It can burn skin and eyes and release oxygen fast in a closed container, so wear splash-proof goggles and nitrile gloves, work in a ventilated room, and keep it away from metals, organic materials and any acid. Use only clean plastic or glass for measuring and mixing, and don't put the concentrate in the spray bottle. Label the spray bottle clearly with "3% H2O2, made [date]" and keep it out of direct light. Peroxide breaks down over time, especially once diluted, so mix a fresh batch for each use instead of storing it for weeks.
A homemade dilution is not an EPA-registered disinfectant, so the contact-time guidance on commercial 3% labels doesn't automatically apply to yours. If the goal is a documented disinfection, a registered product is the safer choice, and the EPA's list of registered disinfectants shows which ones are tested against which germs. Has anyone here made their own dilution from a concentrate, and how did you label and store it?
The dilution math in the post above is right. One caveat on the "disinfection" goal, from the EPA's page on selected EPA-registered disinfectants:
- The contact time is set by the product's label, not by a general rule. EPA says the surface should stay visibly wet for the entire contact time; if it dries sooner, reapply. A 10-minute claim on a surface that dries in 5 means you haven't met it.
- A product should be used against a given germ only if its label makes that claim. A bottle you diluted yourself has no label or registration behind it, so I can't point you to an official contact time for that spray. That's a gap in the documentation, not proof it doesn't work.
So if you need a documented disinfection claim (a sick household, a kitchen after raw meat), an EPA-registered product used exactly as labelled is the safer route. Your diluted spray is better thought of as a cleaner with some sanitizing effect. Also, peroxide degrades in light and over time, so I'd mix small batches.
I didn't find a primary source for a specific contact time at 3% to quote, so I'm leaving that out.
