Is It Important To Know The 21 Foot Rule?

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marine officer aiming pistol on shooting range


You’ve probably heard of the 21 foot rule. How Close is Too Close? 

When gun enthusiasts talk about the 21 foot rule, most are actually referring to the “Tueller Drill,” which wasn’t a rule at all, and which now confuses many well-intentioned gun owners. 

Whether you’re a beginning or experienced shooter, studying this “rule” is an eye-opener. So, where did it come from, and what does it mean for you as a gun owner? 

History and Story of the 21 Foot Rule 

History Behind the Study

Sgt Dennis Tueller, a training officer for the Salt Lake City, Utah police department, had one question in mind – at what distance would a potential attacker armed with a knife or impact weapon pose a lethal threat to a police officer with a holstered sidearm?

He conducted a series of experiments to determine the time an officer would take to react and draw, and effectively shoot in comparison with the time an opponent would dash and strike. Through experimentation, Tueller developed what came to be known as the 21 ft rule. 

His findings were published in an article entitled “How Close is Too Close” in the March 1983 issue of SWAT magazine. Tueller concluded that an armed attacker charging at an officer could quickly clear 21-feet in the time it would take most officers to draw their gun, aim accurately, and fire their weapon. 

Why Was the Study Completed?

Police Officers watching civilians

Firearms instructor, Officer Tueller, designed the 21 foot rule as a training experiment and method to assist officers under training understand “The Reactionary Gap” concept. This concept was all about comparing action versus reaction. 

Given the fact that action taken is always faster than reaction taken, the closer an armed assailant is to an officer, the less time the officer has to react defensively to any potential aggressive action that the assailant makes. 

The Tueller study focused on a simple drill. A “suspect” with an edged weapon stands twenty or so feet away from an officer with a holstered sidearm. Then the suspect runs towards the officer in attack mode. The study’s objective was to determine whether an officer could draw his sidearm and accurately fire at the armed assailant before he or she stabbed him. 

The Reactionary Gap

This is the distance you would need to react decisively and effectively to any given situation. And in this case, Tueller’s experiment showed that if a bad guy armed with a weapon was within 21 feet of you, you would be within his danger zone. 

In other words, the bad guy would cover 21 feet in 1.5 seconds before you could draw your handgun and neutralize the threat. It’s important to understand that there was no forensic testing, examination, scientific oversight of the research model, or reconciliation of data ever done to prove the Tueller drill

Knowing the reactionary gap is the first step in understanding when not to shoot an assailant with a knife. Additionally, using defensive tactics before drawing and firing a handgun is vital for every gun owner to know. 

Various Factors in the Study

The 21 foot rule is not a steadfast rule, but most people seem to get lost in the specifics of disproving Tueller’s individual glimpse at understanding the reactionary gap. The truth is, there are many variables involved in understanding the “rule.”


human brain psychology

Psychophysiology is the study of how the brain influences and affects our physiological function. According to science, we possess both a forebrain and midbrain. Decision-making and cognitive processing happen in the forebrain while sleep, situational awareness, alertness, arousal, and subconscious and trained memories occur in the midbrain. 

When an officer or say you as a shooter experiences a threat, it takes approximately 0.58 seconds to experience the threat or danger and determine if it’s real. Another 0.56 to 1.0 seconds passes before you decide to respond.

When threatened, we respond in five potential ways – defend (fight), posture (point a finger, yell, act aggressively), disengage (retreat), submit (surrender), or become hypervigilant (confusion, panic, freezing, or using excessive force). 

When threatened, your brain automatically fills your body with adrenalin that stimulates your body, endorphins that block pain, and dopamine that further blocks pain. Your body uses these brain chemicals to help you survive an encounter by making you stronger, faster, and more pain-tolerant. 

However, these chemicals can also diminish your performance when you’re under intense stress by causing various problems like loss of near vision, perceptual narrowing, reduced hearing, or even loss of hearing. All these factors reduce your chances of surviving a dangerous encounter. 

When facing a deadly force threat scenario, you’re under intense stress, primarily due to the influence of the brain’s survival chemicals. Due to this, your body’s basal metabolic rate, which is measured by your heart rate, respiration, and blood pressure, climbs significantly in milliseconds. 

This can cause further psychophysiological impairments, which can impair your cognitive process, weapon manipulation, and stress memory recall after an encounter. 

Equipment and Competency

Several factors affect your survival against an attacker. For instance, if you have secured your sidearm in a Level III gun holster, you’ll have a much slower acquisition time to draw and target than someone drawing a gun from a Level I gun holster. 

Your experience and competency with your holster system and combat shooting style will also affect your ability to draw, move away from the line of attack, and accurately fire upon the armed attacker. 

Accuracy of Fire at Close Distance

Countless studies on firearms training have shown that the average officer undertaking static firearms qualification tests can hit 9-10 rings 95% of the time when shooting without moving and in non-timed standing. However, studies of actual OIS incidents have shown that officers can only make accurate hits on a moving assailant 14% of the time in a life or death situation from 2-10 feet away. 

In the same scenario, assailants were able to successfully engage and hit the officers up to 68% of the time with the same distance. Accuracy of fire within close range plays a critical role in determining the reactionary gap needed for self-defense. 

Perception lag

After the average officer gets on target, it takes them around 0.56 seconds to make the critical decision on whether to start shooting. However, the same officer takes approximately 0.33 seconds per trigger pull to fire. Remember that any deadly-force scenario evolves rapidly. The officer will take 0.55 to 0.58 seconds to realize that the threat has passed to stop shooting. 

This is due to a psychophysiological dynamic called perception action-reaction lag time. That explains why action is always faster than reaction. This perception lag also explains why suspects shot in such scenarios often have entry wounds on their sides or back, whereas the officers who shot them explain that the suspects were facing them when they fired.

How Does this Apply to You as a Gun Owner?

The Tueller drill study had one goal in mind – to understand how close is too close when facing an assailant with a knife. The study pushed firearm trainers to rethink this issue. It also significantly changed how police departments and trainers viewed edged and blunt instrument attacks. 

The 21 foot rule is by no means an absolute defense measure. But it does give a practical way to look at the different dynamics of self-defense for civilian gun owners. With the demonstration of the Tueller Drill, participation even works better in helping shooters comprehend the facts. 

The drill establishes a flashing red warning light. But, if you do shoot somebody, you must be prepared to fully justify your actions, including why the situation was life-threatening and why you couldn’t delay your reaction. 

Tips If You’re in a Real-Life Self-Defense Situation

man pulling pistol from back waistband

In numerous demonstrations of the 21 foot rule, tests with hundreds of officers have consistently shown that in most cases, a minimum reactionary gap of 21 feet is required to react and deliver at least two rounds and have enough time to move off the attacker’s path. 

You can significantly change your actual reactionary gap in terms of the time an attacker takes to reach you, and the time it takes for you to react. Unfortunately, most of the officer training and self-defense training for civilians makes it difficult to prepare for a real-life situation. 

Shooters spend most of their time training in a standstill position, whereas if you encounter an enemy, you’ll most likely be moving. Another reality is that you don’t stop fighting when you shoot the assailant because it takes time before the wounded assailant loses the blood volume necessary to shut down their system. 

Despite this, Officer Tueller called on officers to use defensive strategies and tactics when confronted with a person with a knife. These tactics can apply in civilian self-defense training. So, if you’re in a real-life self-defense situation, here are some tips you should know:

  • First, you need to develop and maintain a healthy level of tactical alertness. If you spot life-threatening or danger signs early enough, consider avoiding a confrontation altogether. A tactical withdrawal after analyzing the situation is an option. 
  • Next, if your “early warning system” tells you that a possible lethal confrontation is imminent, you’ll want to place yourself in the best tactical position available. You could move to cover if there’s any closeby, draw your weapon, and start to plan your next move. 
  • Why use cover? Because you want to make it hard for your attacker to get to you. Anything that comes in between you and your attacker will slow him or her down and buy you more time – this could be furniture, an elevation change, a car, or any other object. 
  • Don’t get caught flat-footed, but don’t backpedal or sidestep. Instead, move at a 45-degree angle or laterally towards the charging attacker to buy time to react. An analysis of the situation at hand may help you react quickly. 
  • If you’re not used to smoothly drawing and making hits quickly under stress, it will take you considerably longer than 1.5 seconds to make the first hit on your assailant. So practice, practice, practice.

Is This Applicable in a Real-Life Situation?

The Tueller drill is a series of self-defense exercises that demonstrate what could happen in a scenario where an officer or a civilian faces an attacker armed with a knife or other edged weapon. While many variables affect the outcome in this situation, the drill is all about awareness and drawing and firing quickly.  

But in a real-life situation, never stand still or face down a charging attacker. Instead, you should move to the nearest cover or shoot on the move. The 21 foot rule is simply a situational awareness tool that tells you to be on your toes and be alert of potential threat possibilities while emphasizing the need to prepare to respond. 


Think of the good guy with a gun versus the bad guy with a knife. Most of us will say the man with the gun can’t lose. But the truth is, a great deal will depend on the shooter’s ability with the gun and the proximity of the attacker. 

The 21 foot rule demonstrates that an armed attacker at 21 feet is well within your Danger Zone. While it’s definitely not a completely accurate way to describe every potential scenario of a knife-wielding threat approaching a shooter, practicing the Tueller principle in self-defense training can help improve your judgment and the reaction time when a threat is approaching. 

Practicing the Tueller drill to improve your draw time and accurate shot placement is one of the many effective training drills you can run through as a gun owner.

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Hi there, I'm Brady and I'm the owner of I have been an avid gun enthusiast and hunter since I moved to the Midwest over 15 years ago. It's my passion to share my knowledge and expertise to help you find the best guns in your price range.

2 thoughts on “Is It Important To Know The 21 Foot Rule?”

  1. Extremely enlightened me on the amount of time between reacting and reaction and how close is too close. Valuable information for beginners.


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