How to Make a 10% Bleach Solution (1:10 Dilution)

A “10% bleach solution” is a 1:10 dilution: 1 part household bleach plus 9 parts water, which makes 10 parts in total. The strength you end up with depends on the bleach you start from. CDC describes common US household bleach as an aqueous solution of 5.25%-6.15% sodium hypochlorite (52,500-61,500 ppm available chlorine) and states that a 1:10 dilution of it provides about 5,250-6,150 ppm. As simple arithmetic on those figures, that is roughly 0.5% sodium hypochlorite. This guide covers how to prepare that dilution for lab surface disinfection, what it is used for, and what goes wrong.

What “10% bleach” means, and why the product strength matters

“10%” describes how much of the final liquid is bleach product, not how much of it is sodium hypochlorite. Ten percent product (1:10) of a bleach labelled 5.25%-6.15% sodium hypochlorite gives the CDC figure of about 5,250-6,150 ppm available chlorine. If your product carries a different percentage of sodium hypochlorite on its label, the same 1:10 mix gives a different final strength (the result scales in proportion), so read the percentage on the label of the bottle you are using before you mix.

Dilution	Mix (bleach : water)	Approx. available chlorine from 5.25%-6.15% bleach	Basis
Undiluted product	–	52,500-61,500 ppm	Stated by CDC
1:10	1 part + 9 parts	about 5,250-6,150 ppm	Stated by CDC
1:100	1 part + 99 parts	about 525-615 ppm	Arithmetic from the 1:10 figure
1:1,000	1 part + 999 parts	about 53-62 ppm	Stated by CDC

What you need

• Household bleach whose label shows its percentage of sodium hypochlorite (CDC describes 5.25%-6.15% as the common US range).
• Water, and a clean container that can be closed.
• A measuring cylinder or other graduated container, so the parts are measured and not estimated.
• The eye and skin protection your lab’s SOP requires. CDC lists ocular irritation and oropharyngeal, esophageal and gastric burns among the hazards of hypochlorite.
• A way to record the date and the dilution on the container (see the stability section below for why).

Steps

1. Read the sodium hypochlorite percentage on the bleach label and write it down.
2. Decide the total volume you need and divide it by 10. One tenth is bleach, nine tenths is water. For 1 litre, that is 100 mL bleach and 900 mL water.
3. Measure the water and the bleach separately, with the protection your SOP requires.
4. Combine them in the container, close it, and mix gently.
5. Label the container with “1:10 bleach”, the product’s percentage and the date prepared.
6. Use it on a surface that has already been cleaned, following your lab’s SOP for contact time. The 1:10 level in CDC’s guidance is for large blood spills, applied after the spill is cleaned (see below).

When is 1:10 the right strength?

CDC recommends a 1:10 to 1:100 dilution of 5.25%-6.15% sodium hypochlorite for blood spills. In that guidance, small drops of blood on noncritical surfaces are handled at 1:100, and large spills at a 1:10 final concentration, applied only after the surface has been cleaned, because hypochlorites are substantially inactivated in the presence of blood. For a spill with possible sharps, CDC describes decontaminating the surface first, then cleaning and disinfecting at 1:10 final concentration. For lab-specific spill steps inside or outside a cabinet, see biological spill response inside and outside a biosafety cabinet, and for how bleach compares with other agents, see types of disinfectants.

OSHA’s bloodborne pathogens standard (29 CFR 1910.1030(d)(4)(ii)) requires that equipment and environmental and working surfaces be cleaned and decontaminated after contact with blood or other potentially infectious materials, and that this be done with “an appropriate disinfectant”. The regulation does not name a dilution, so 1:10 is not an OSHA-mandated figure; your institution’s exposure control plan and SOPs decide which disinfectant and strength apply.

How to make a 5% bleach solution

This phrase is ambiguous. If “5%” means 5% bleach product in water, that is a 1:20 mix (1 part bleach + 19 parts water), which as arithmetic from the CDC 1:10 figure is about half the strength of a 1:10 solution (roughly 2,600-3,100 ppm from 5.25%-6.15% bleach). If it means 5% sodium hypochlorite, the undiluted household bleach CDC describes (5.25%-6.15%) is already around that strength and needs no dilution. CDC’s blood-spill guidance names 1:10, 1:100 and 1:1,000 dilutions and does not give a 1:20 recipe, so check which strength your SOP calls for before preparing it.

What can go wrong

The solution loses strength over time

CDC reports that hypochlorite solutions made with tap water at pH above 8 and kept in closed, opaque plastic containers can lose up to 40%-50% of their free available chlorine over one month. As an example of planning for that loss, CDC notes that to have 500 ppm on day 30, you would prepare 1,000 ppm at time zero. The same CDC text says a solution stored in a closed brown bottle does not decompose after 30 days. Recording the preparation date on the container lets whoever picks it up judge how old it is.

Mixing with ammonia or acids releases chlorine gas

CDC lists the release of toxic chlorine gas when hypochlorite is mixed with ammonia or acid (for example, household cleaning agents) as a hazard, and also names bis(chloromethyl) ether formation with formaldehyde. Do not combine bleach with other cleaners or store it next to them; see chemical storage compatibility and segregation rules.

Corrosion of metals

CDC lists corrosiveness to metals at high concentrations (above 500 ppm) as a limitation of hypochlorite. A 1:10 solution is well above that level. For cabinet surfaces, see biosafety cabinet cleaning and decontamination procedures.

Applying it to a dirty surface

Because hypochlorites are substantially inactivated in the presence of blood, a surface with visible blood should be cleaned before the 1:10 solution is applied for the final disinfection step, as described above. For choosing between agents and checking surface compatibility, see surface disinfectant selection, contact time and material compatibility.

When to get professional help

• Contact your institution’s biosafety officer or environmental health and safety office if a spill involves an agent or quantity your SOP does not cover, or if you are unsure which disinfectant and strength your biosafety level requires.
• If bleach contacts eyes or skin, or is swallowed or inhaled, follow your site’s emergency and exposure procedure and seek medical attention.
• Prions are a separate case; see prion decontamination protocols.

FAQ

How do I make a 10% bleach solution?

Mix 1 part household bleach with 9 parts water (a 1:10 dilution). For 1 litre, use 100 mL bleach and 900 mL water. From bleach labelled 5.25%-6.15% sodium hypochlorite, CDC states this provides about 5,250-6,150 ppm.

Is a 10% bleach solution the same as 10% sodium hypochlorite?

No. It is 10% bleach product in the final liquid. With a 5.25%-6.15% product, the sodium hypochlorite content of the mix is roughly 0.5% (arithmetic from CDC’s ppm figures).

How do I make a 5% bleach solution?

See the 5% section above: as 5% product, it is 1 part bleach to 19 parts water, about half the strength of 1:10 by arithmetic. Confirm with your SOP which one is meant.

How long does a diluted bleach solution last?

CDC reports that tap-water solutions kept in closed opaque plastic containers can lose up to 40%-50% of their free available chlorine in a month, and that a solution in a closed brown bottle did not decompose over 30 days. Follow your lab’s SOP for how often to prepare it.

Does OSHA require 1:10 bleach?

No. 29 CFR 1910.1030 requires cleaning and decontamination with an appropriate disinfectant and names no dilution.

Sources

• CDC, Chemical Disinfectants (Guideline for Disinfection and Sterilization in Healthcare Facilities), checked 2026-10-29.
• eCFR, 29 CFR 1910.1030, Bloodborne pathogens, paragraph (d)(4)(ii), checked 2026-10-29.