Department of Health

Chlorine-based (sodium hypochlorite) sanitisers/disinfectants (e.g. plain, unscented household bleach) should be used in outbreak situations, as other sanitisers have very little effect on destroying viruses such as Norovirus.

This easy-to-use calculator tells you how much chlorine-based (sodium hypochlorite) sanitiser/disinfectant to dilute with water to get the desired concentration (parts per million) of chlorine solution. This chlorine calculator is intended for use by local government environmental health officers, health and residential care facilities, children's services centres and camp operators.

These calculations are to be used a guide only. For information about how to dilute specific products please refer to the relevant Material Safety Data Sheet (MSDS) for the specific chemical disinfectant being used, or contact your supplier or manufacturer of the product.


  • Ensure that all environmental surfaces and hand touch surfaces ahev been cleaned with hot water and detergent (so they are free of vomit, faeces or any organic matter) before the chlorine solution is applied.
  • Sufficient time is required to kill the virus - at least 10 minutes contact time.
  • Chlorine (sodium hypochlorite) soutions must be made up prior to use as the chlorine deteriorates over time.
  • Chlorine (sodium hypochlorite) solutions should be used mainly on hard, non-porous surfaces.
  • Check the expiration dates of your bleach or chemical sanitiser to ensure the active ingredients are still effective.
  • Ensure your staff know how to correctly use your chlorine (sodium hypochlorite_ solution or chemical sanitiser.

Important safety notes for use of chlorine (sodium hypochlorite) solutions:

  • Use gloves and wear protective eyewear when preparing chlorine (sodium hypochlorite) solutions.
  • When using chlorine bleach, it is safer to add chlorine to water - do not add water to chlorine.
  • Do not use hot water to make up chlorine solutions - cold water is safer.
  • Do not mix with any other chemical.
  • Mix in a well ventilated room.
  • Follow safety, storage and handling instructions on all bleach and chamical containers.
  • Use chlorine carefully as it is corrosive to metals, damages fabrics/textiles and some plastics and may irritate the skin, nose and lungs.
  • Ensure that all chemicals are labelled and stored seperately so as to prevent the likelihood of food being contaminated.
  • Bleach solutions should NEVER be applied using a spray bottle. This is an occupational health and safety hazard.
  • Milton tablets are not validated for use as a surface disinfectant and are not recommended for this purpose.

Chlorine dilutions calculator

Reviewed 05 March 2019


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