Survival Rule of 3 | The Ultimate Guide
Survival in the wilderness is a skill that every outdoor enthusiast, adventurer, and prepper should master. The Survival Rule of 3 provides a simple yet crucial framework for prioritizing your actions in a survival situation. When you understand and apply these rules, you increase your chances of surviving in the face of adversity.
I’ve used the rule in the military, in my preparedness planning, and in practicing wilderness survival. It helps me make snap decisions in the field and prioritize risks quickly.
Besides the meaning of the rule itself, I also dive into what each part of the rule means for survival. There are also a few additions that have been made to the rule, and we examine those for merit.
Contents (Jump to a section)
What is the Survival Rule of 3?
The Survival Rule of 3, or “rule of threes”, is a rule of thumb that describes the basic survival rules using the number three.
The rule says that you can survive:
- 3 minutes without air
- 3 hours without shelter
- 3 days without water
- 3 weeks without food
The order of these determines what you should prioritize in a survival situation. First, you need to be able to breathe. Next, you need to have a way to shelter yourself from the elements. Then you will need to acquire a source of water. Finally, you will need to forage or hunt for food.
Each rule assumes that you are meeting the requirement above it. For example, you can’t survive 3 weeks without food unless you have water. You can’t survive 3 hours without shelter unless you have air, etc.
The survival rule of 3 may seem simplistic, but it can help you make split-second decisions in a survival situation. Mulling over whether to gather food or build a makeshift shelter can waste valuable time. The rule is simplistic, so it can be easy to remember and helpful when you are stressed in a survival situation.
The rule is not exact. Many people can hold their breath for longer than three minutes. The shelter rule has a lot of variances based on the environmental conditions. We’ll review each rule’s accuracy and how to apply it to survival below.
Drop the Air – Wilderness survival often drops the Air part of the rule, making it even simpler: 3 priorities (shelter, water, and food) that have 3 time limits.
Air
The Survival Rule of Threes states you can survive 3 minutes without air.
You can’t make it very long without air. Oxygen is the key ingredient that we inhale, circulate through our bloodstream, and power our cells.
Three minutes may not seem like a long time, but it is a general guideline. The world record for holding is a whopping 24 minutes and 3 seconds- much longer than 3 minutes! This was accomplished by Aleix Segura Vendrell, a professional free diver from Spain. Holding your breath underwater works a little differently than on land, though. Humans have a little-known reflex that makes it easier to hold their breath underwater- a reflex that helps us avoid drowning.
Survival Tips for Air
Drowning isn’t the only way you can die without air. Any situation that cuts off your breathing can pose a risk of immediate death, even if it seems harmless. One of the most common examples: Choking on food kills thousands of people every year. It is the fourth leading cause of unintentional injury death.
Choking is a very direct way to test how long you can survive without air. It catches you unprepared (and not underwater). Four to six minutes is about how long you have, according to medical experts. Irreversible brain death will occur within 10 minutes if you are unable to breathe or receive medical assistance.
Because it is so important to our function and survival, you need to learn basic first aid. One of the first things you learn in CPR is the ABC priorities:
- Airway – Check to see if anything is blocking air from getting into the lungs, like the tongue or a foreign object.
- Breathing – Check for signs of breathing: look for chest rising, listen for breathing noises, and feel for breath movement.
- Circulation – Check for a pulse.
Being prepared with CPR knowledge and knowing how to do the Heimlich maneuver is very important, according to the survival rule of 3.
Besides fluke accidents, like choking or drowning, there are several survivalist scenarios that can attack your airways. CBRN (Chemical, Biological, Radiological, and Nuclear) attacks and accidents can cause fatal damage through inhalation. N95 masks, at the very least, can protect you in the face of pandemics. A full-faced respirator (gas mask) with a purified air attachment (PAPR) would be the best bet for the others.
Even still, some disasters- like fire- require that you leave the area. A gas mask will not protect you from smoke inhalation. Full-service SCBA equipment is used by firefighters in these situations, and that is not practical for the public to keep it on hand.
Shelter
The Survival Rule of Threes says you can survive 3 hours without shelter.
This is one of the most conditional parts of the rule- your shelter needs depend heavily on environmental factors.
Exposure is the leading cause of death in the wilderness. Extreme heat and cold can be brutal on the human body, which is why we have adopted such a wide range of tools and shelters to protect ourselves.
Survival Tips for Shelter
Shelter from the elements doesn’t have to be a literal bushcraft shelter. This category covers everything that stands between you and the elements, which can include:
- Tarps
- Makeshift shelters
- Bivvys
- Sleeping Bags
- Tents
- Your home
- Umbrellas
- Campfires
- Clothes
- Shoes
You may not initially think of an umbrella or campfire as a type of ‘shelter’, but they protect you from the elements.
Similarly, clothes are a barrier between your body and the elements. On the popular survival TV show series, Naked and Afraid, contestants have to strip down for the survival challenge. This doesn’t just add awkward drama that makes for good TV- it also makes it more difficult to survive. Contestants have to figure out how to keep a fire going, huddle for warmth, and even ward off insects.
You may need to get creative yourself if you need shelter in a survival situation and have no equipment. Bushcraft is one of the leading wilderness survival hobbies, and it covers building shelters in the wild.
Water
The Survival Rule of Threes states that you can survive 3 days without water.
Thirst is uncomfortable. Dehydration is painful. And beyond that? Fatal.
Going without water can quickly become a life-threatening problem. This makes sense because our bodies are mostly water. Most people know that we are made up of about 60% water, but this varies quite a bit by organ:
- Brain = 73% water
- Lungs = 83% water
- Muscles = 79% water
- Skin = 64% water
- Bones = 31% water
Babies are especially watery, being over 78% water. Women are about 5% less water than men, on average.
The body’s thirst mechanism lags behind dehydration, so by the time you are thirsty, your body is already feeling some effects. Slight dehydration affects your mood, memory, attention span, and coordination. Then your kidneys start to retain water, reducing your urge to urinate. From this point forward, your blood starts to thicken with less water, and your cardiovascular system can become stressed: lightheadedness and even fainting will occur. Quickly after this, organs can begin shutting down.
Scientists have also said that the average time a human can last without water is closer to 100 hours (a little over 4 days), as opposed to 3 days. This is assuming room temperature in a lab setting. High heat will drastically cut this down to below two days. Cold weather can extend this beyond 5 days.
Your level of activity and the environment around you can greatly affect how long you can go without water. Extreme temperatures can make your body require more water, especially if you are active.
Survival Tips for Water
There is a wide range of guidance on how much water you need each day to survive, but the most sponsored guidance from doctors and scientists is about half a gallon each day (2 Liters). They say this should be stretched out in 8 servings of 8-ounce cups (8×8) so that you have a steady supply of water throughout the day.
Supply interruptions and utility shutoffs are a few of the ways large groups of people could start running short of water. With a water shortage, collection methods will come in handy, such as capturing and filtering your own water, rainwater collection, and distilling from the air.
All of these reasons explain why water containers and purification methods are important for survival kits. You can see exactly how much water you’ll need with our water storage guide.
Food
The Survival Rule of Threes tells us we can survive 3 weeks without food.
Hunger can be brutal, but starvation is deadly. Although it is the last priority for the survival rule of 3, food is still important and on the list. Even though our bodies can tolerate long periods without food, it can be one of the most difficult things to find in an emergency or disaster situation.
This is also one part of the rule that could be exaggerated: experts agree that fourteen days is the best approximation for how long you can survive without food.
Supply chain interruptions can sever food sources from their destination across any country. The modern world is powered by supermarkets that rely on these delicate supply chains, and variances in either demand or supply are quickly seen.
Survival Tips for Food
A food storage plan is very important for prepping and survival. There are many methods for storing or obtaining food, from stashing canned goods in your pantry to picking up new hobbies, like gardening.
The plan also depends heavily on whether you are going somewhere or staying put. Typical emergency plans ask you to put away 72 hours’ worth of food, but targeting the ‘rule of three’ is a better idea: aim for three weeks instead of three days.
Limits to the Survival Rule of 3
Because the survival rule of three isn’t exact, the actual time for each area it covers differs. You can come in below or above the 3, depending on the situation, so don’t go setting any timers.
Some of the exceptions have been proven to go much longer:
- A German diver held his breath for 22 minutes and 22 seconds
- Shelter requirements depend on the weather and the environment
- An Austrian man survived for 18 days without water
- A hunger strike participant lasted 74 days without food, verified by a doctor
These anecdotes blow up the idea that the survival rule of three is consistent for everyone in any situation.
Variations to the Rule
The rule seemed a little too basic to some because a few have tacked on some extra variations/rules to ‘spice it up.’ I’m not partial to over-complicating a simple rule, but you can decide for yourself. A few extra ‘rule of threes’ include:
You can survive:
- 3 seconds before making a survival decision
- 3 minutes in icy water
- 3 months without companionship
- 3 months without hope (I have also seen this as 3 seconds)
The bullet about hope is a throwback to the saying:
“Man can live 40 days without food, three days without water, eight minutes without air… but only one second without hope.” – Hal Lindsey
This is less catchy and harder to remember than the survival rule of threes, and I’m not completely sold on the ‘hope’ part. Although I agree that hope is important in a survival situation, it is less tangible than the other requirements for the human body.
These extra rules are less concrete, and the whole thing gets further away from the original intent as you add more rules. I prefer the original, simple Survival Rule of 3, but feel free to chime in with any additions that you prefer in the comment section.
How I Apply the Rule
I keep the survival rule of three in mind when I conduct risk assessments, plan and pack survival kits, and work on my wilderness survival training. Conducting large-scale risk assessments has been a pet project of mine since I started TruePrepper almost a decade ago.
The idea behind this entire website was to create a threat-based prepping resource that hinged on risk analysis. This ended up being a much larger task than I imagined, as threats continue to evolve and they aren’t the same for everyone. The result was one of my first pages published: the Threat List. No matter the disaster, emergency, or SHTF situation listed, you’ll see elements of the rule of three at work in the mitigation plans.
When I go to practice my wilderness survival skills or bushcraft, I go back to the abridged version of the survival rule of three, considering just shelter, water, and food. For shelter, I either have my tent or tarp and the survival clothes on my back. I also start a fire for warmth if needed, which can also help purify water. Water being the next priority, I usually head downhill to find a water source to purify. Lastly, I usually bring food with me because it can be difficult to find if you are not specifically hunting, foraging, or trapping.
When I create survival kits, I specifically label and organize gear to address the survival rule of three categories.
Building a Survival Kit
Survival kits are full of gear that is meant to address the challenges posed by the survival rule of three. I use color-coding organization with my gear for easy identification and inventory.
Air (PPE, First Aid)
PPE, or personal protective equipment, helps protect your body. It falls in the same category of clothing, but is more specifically used for protection. Gloves, earplugs, and other gear fall in this category, but for the survival rule of three, we’re focused on protecting our airway.
The gear that addresses this is masks; whether you choose to go with an N95 mask or a full-face respirator depends on the risks you might encounter.
First aid kits (stand-alone or nested inside a survival kit) also offer a few tools that help maintain your airway if you are injured. These usually include nasopharyngeal airways and chest seals.
Shelter
Whether you are making a bug out bag or a home survival kit, shelter is one of the highest priority categories. There is a wide range of gear to either create a shelter or quickly repair your home in an emergency. Gear typically includes tarps, tents, and more. Fire-starting tools and clothing are also categories that could help, since they can provide warmth.
Water
Spanning from EDC lists to niche threats, water collection and purification is always a concern. Many emergency plans have you store water, but you’ll run out quickly, using at least a gallon per day.
Water is also extremely heavy, at 8.345 pounds per gallon. Carrying just a day’s worth of water in a mobile survival kit will wear you out over any distance.
Finding ways to collect water and purify it are important, with tools found in almost every survival kit, including:
- Water bottles (steel preferred, for boiling)
- Water purification tablets
- Water filters
These are all much smaller and lighter than carrying actual water around or dedicating huge storage tanks. Rain barrels are also common for in-place survival kits, where they are legal.
Food
Food can be incredibly hard to come by if you are unprepared. In-place survival kits rely on canned food, emergency food supply kits, and gardens for food. Mobile survival kits, like get home bags, rely on portable options including:
- Emergency food bars – old school boat rations, but upgraded
- MREs (Meal, Ready to Eat) – a military staple
Besides the four survival focuses derived from the survival rule of three, survival kits also include gear for self-protection, communication, navigation, and more. Survival is never simple, even if we have a simple rule to address our most pressing needs.
Sources and References
I’m not a scientist, so I dug up some sources that helped me compare scientific studies with the survival rule of three to compare accuracy. These articles and scientific studies helped me profile the risks associated with each component of the rule.
Baker, D., et al. (2013). The Psychology of Hunger. American Psychological Association. Volume 44. Issue 9. Page 56. (Source)
Castellini, M., et al. (1992). The Biochemistry of Natural Fasting at Its Limits. Experientia. Volume 48. Pages 575 – 582. (Source)
Keys, A., et al. (1950). The Biology of Human Starvation. The University of Minnesota Press. Volume 1. (Source)
Lieberson, A. (2004). How Long Can a Person Survive Without Food? Scientific American. (Source)
Lipscombe-Southwell, A. (2023). What’s the longest a human can hold their breath underwater? BBC Science Focus. (Source)
Mundel, T. (2016). Here’s What Happens to Your Body When You’re Dehydrated. Science Alert. (Source)
National Safety Council. (2020). Choking Prevention and Rescue Tips. (Source)
Stewart, W., et al. (1973). Features of a successful therapeutic fast of 382 days’ duration. Postgraduate Medical Journal. Volume 49. Issue 569. Pages 203 – 209. (Source)
USGS. (2020). The Water in You: Water and the Human Body. (Source)
The Final Word
The survival rule of 3 is a great rule to lean on when you need to make a split-second decision during a disaster or emergency. It is also a good rule of thumb to plan around when developing prepping and survival kits. It gives us foundational survival values and sound risk management in an easy-to-remember ‘rule’.
Beyond these guides, we also test and recommend a wide variety of tried-and-true equipment for a wide range of budgets. This should help you on your way to preparedness and improve your survivability with all four sections of the survival rule of 3.
Here are some of the guides our subscribers have found especially useful:
- Two is One and One is None | The Power of Redundancy
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- Bug Out Bag List | 44 BOB Essentials
Keep exploring, stay prepared, and be safe.
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Superb article. For years, I have had my own way of remembering:
3 = A S W F / M H D W
Obvious there are always variables but it’s basic.
¿”3 = A S W F / M H D W”? ¡WTF!
OK, “A S W F” seems to be self-explanatory, but many would find “M H D W” to be unintelligible. A translation would be helpful.
MHDW = Minutes, Hours, Days, Weeks