Rule of threes (survival)

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Training in use of a liferaft – the rule will apply when exposed at sea

In survival, the rule of threes involves the priorities in order to survive.[1][2][3] The rule, depending on the place where one lives, may allow people to effectively prepare for emergencies[4] and determine decision-making in case of injury or danger posed by the environment.[1]


Normally, the rule of threes contains the following:

  • You can survive three minutes without breathable air (unconsciousness), or in icy water.
  • You can survive three hours in a harsh environment (extreme heat or cold).
  • You can survive three days without drinkable water.
  • You can survive three weeks without food.

Each line assumes that the one(s) before it are met. For example, if you have a large quantity of food and water yet are exposed to the environment, then the harsh conditions rule applies. The rule may sometimes be useful in determining the order of priority when in a life-threatening situation, and is a generalization (or rule of thumb), not scientifically accurate.[5]

Additional generalizations may be presented with the rule, though they are not considered part of the "Rule of threes" and are also not scientifically accurate. For example, it might be said that it takes a three-second psychological reaction time to make a decision during an emergency,[1] or that an individual can last three months without hope.[6][5][7]


  1. ^ a b c Towell, Colin (2011). Essential Survival Skills. Penguin. ISBN 978-0-7566-7338-3.
  2. ^ "Survival and the Rule of Threes (What it all Means)". UK Survival Guides.
  3. ^ "Wilderness Survival Rules of 3 - Air, Shelter, Water & Food". 29 May 2012.
  4. ^ Williams, Scott B. (2010). Bug Out: The Complete Plan for Escaping a Catastrophic Disaster Before It's Too Late. Berkeley, CA: Ulysses Press. p. 26. ISBN 978-1-56975-781-9.
  5. ^ a b "The Survival Rule of 3 - Air, Shelter, Water, & Food". TruePrepper. 3 April 2020.
  6. ^ Dorrell, Darrell D.; Gadawski, Gregory A. (2012). Financial Forensics Body of Knowledge. Hoboken, NJ: John Wiley & Sons. p. 506. ISBN 978-0-470-88085-2.
  7. ^ Nowka, James D. (2013-05-28). Prepper's Guide to Surviving Natural Disasters: How to Prepare for Real-World Emergencies. Penguin. ISBN 978-1-4402-3584-9.