The Rule of Threes

Several years ago, I went on a guided backpacking trip in Great Smoky Mountains National Park with A Walk in the Woods.  I had a great time and learned a lot.  One of the most important lessons I took away from that trip was “The Rule of Threes.”  This simple rule has become the cornerstone of my philosophy for lightweight backpacking and enjoying the outdoors safely.

The Rule of Threes

“The Rule of Threes” is a simple guide for remembering survival priorities.  The Rule of Threes applies to the average person in average conditions.  The four points are guidelines, not hard and fast rules.

  • You can survive for 3 minutes without oxygen
  • You can survive for 3 hours without shelter
  • You can survive for 3 days without water
  • You can survive for 3 weeks without food

You Can Survive for 3 Minutes Without Oxygen

When I first heard this, I didn’t think it was important.  I don’t spend a lot of time under water or in outer space, so oxygen shouldn’t be an issue.  As I’ve thought more about it, I’ve realized how important this rule is for preparing for any activity outdoors.  Am I ready to aid a member of my group who has stopped breathing?  If anyone in my group has asthma, are they carrying an inhaler? If anyone has severe allergies, do they have an EpiPen? It is important to think of these things before heading out into the woods.  Once your friend is lying there with a blocked airway, you only have three minutes.

You Can Survive for 3 Hours Without Shelter

When it’s nice out and you’re in good health, you can stay outside all day. What happens when you fall and break an ankle? What if there is an unexpected rainstorm? What would you do if you were lost and had to spend an unplanned night in the woods? Panic, illness, injury, and environmental conditions can quickly wear down your physical and mental resources.

CampingJay practices setting p a poncho as an emergency shelter.
CampingJay practices setting p a poncho as an emergency shelter.

Most people think about shelter as a tent, cabin, or improvised structure.  I include everything that protects your body from the environment: sunscreen, insulation, rainwear, and wind protection.  The clothing and shelter I carry with me varies seasonally, but it does not vary based on the length of my trip.  I carry the same gear for a summer day hike that I do for a 5 day backpacking adventure during the same season.

You Can Survive for 3 Days Without Water

Your body is 80% water. You need water to carry out almost every life function.  Water, in the form of blood, carries nutrition and oxygen though-out your body. In the form of urine, it expels chemical waste products. In the form of sweat it helps keep you cool. Water lubricates your eyes, joints, muscles, and other moving parts.  Without water, there is no life.

Melting snow while on a short winter day hike. Disregard the unfrozen lake behind me.
Melting snow while on a short winter day hike. Disregard the unfrozen lake behind me.

Fortunately, a body at rest uses water slowly.  If you’re in an emergency and you stay calm, you can get by for a while without water.  Of course, surviving without water depends upon having proper shelter. If you’re exposed to the hot sun with no protection, you may need water a lot sooner than three days.

Whenever I go out into the woods, I bring at least a liter of fresh drinking water. I also bring some means of replenishing that water.  Usually, this is as simple as a few dropper bottles of Aqua Mira. With a container, some kind of filter or purifier, and a few skills, you can survive an extended period after your water supply has run out.

You Can Survive for 3 Weeks Without Food

This one makes me laugh. On all the survival shows, the first thing our hero demonstrates is how to eat bugs or bite the head off a snake. They do this for ratings.

My homemade trail mix is a combination of nuts, dried fruit, and chocolate covered espresso beans.
My homemade trail mix is a combination of nuts, dried fruit, and chocolate covered espresso beans.

Food is important. You need energy to move, to think, to breath, and to pump blood.  You also need to ingest fresh resources to rebuild damaged cells or tissues. You should never go into the wilderness without enough food for the time you plan on spending, and then a little more.  If you run out, don’t panic.  If you’re not running around like a nut, you probably won’t exhaust your energy reserve.

Being Prepared

Surviving an emergency in the wilderness starts at home.  It starts with the decision to plan your trip properly. Have you considered local regulations where you’re going? Have you considered environmental conditions like weather and terrain? Are you giving yourself enough time to complete your goal and return safely? Do you have the knowledge and skills you need? Do members of your group have any serious medical conditions or allergies? Are they ready for the trip? Does anyone at home know where you’re going, when you’ll be back, or what to do if they don’t hear from you?


“The Rule of Threes” is the foundation for my philosophy for enjoying the outdoors safely.  I consider its tenants when preparing for each trip I go on. When considering a destination, I weigh the resources that will be available against what I will need to bring with me. When packing, I check each item’s ability to withstand the environment I’m going into.  I’m also extremely familiar with all of my gear.  I know how to use each item, what its meant to do, and what it can do if necessary. Above all else, I practice basic skills like navigation, first aid, and bushcraft.  Not only will these basic skills be necessary if there is an emergency, but I believe they are the best way to avoid an emergency.

Good gear is small and light.  You may be tempted to leave heavy or bulky gear at home. If you’re basic gear is small and light, you’re more likely to always carry it with you.


What are your priorities for preparing for an emergency in the wilderness? You can answer in the comments section below.


3 thoughts on “The Rule of Threes”

  1. HAM radio, sat phone, 10 extra gallons of fuel in Septor gas cans. Also, it doesn’t hurt to bring extra coolant, motor oil and gear oil.

  2. Those are all valid points, Andreas. Being able to keep your vehicle moving will play a vital factor in deciding whether to stay put and wait for rescue, or to try to keep moving. Having the right supplies allows you to make the decision rather than being forced into a decision.

    I would go further, and add the following: because a motorized vehicle can potentially carry you further from potential rescue than a person would usually be on foot, you must be prepared to last longer in the wild should your vehicle break down. That is assuming you are not in an area regularly patrolled.

    Carrying a HAM radio or satellite phone may also be considered when planning to spend several days outside of the reach of civilization. I would arrange standard contact intervals with someone at home and give them instructions on what to do if you don’t report in.

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