The Tueller Principle

A knife-armed attacker 21 feet away can kill you before you can draw and shoot. Whether the attacker is young, old, fat, thin, fit, sedentary, male, female, makes little difference. From a standing start, an attacker can cover 21 feet in 1.5 to 2.0 seconds. That is how long it takes you to draw and shoot. Watch the video below. Remember it. Post a comment that you watched it. You may someday need to prove in court that you knew this fact, and that is why you fired.

Dennis Tueller, the Scientist

In the fall of 1982, Sgt. Dennis Tueller was a homicide investigator with the Salt Lake City Police Department. He was newly assigned to teach combat pistol to the other officers. During a discussion on attacks with contact weapons (knives, machetes, hammers, clubs), a student asked how close an officer should let an attacker get before shooting. Like thousands of firearms instructors before him, Sgt. Tueller had no precise idea. Unlike those thousands, he decided to find out rather than guess. He experimented and recorded the results.

Tueller’s findings are a rare example of scientific inquiry at its finest. There are two reasons for their epistemological elegance. First, the results are unbelievable at first glance. Second, their accuracy is so easily replicated that they persuade even the most hostile skeptic. Try it yourself.

Encouraged by fellow instructors at Gunsite Academy in Arizona, Tueller published his findings in “How Close is Too Close” in the March 1983 issue of S.W.A.T. magazine. That article, and Tueller’s lectures and classes after his promotion to Lieutenant and retirement from law enforcement, have revolutionized pistol self-defense for instructors as well as students.

Time Yourself

Have a friend or spouse with a stopwatch yell “go!” and then measure how long it takes you to draw and shoot a stationary target. By dry-firing, you can do this in your living room. Better would be to dry-fire with a training laser to make sure that you hit the target. Best would be to do it at the range with a steel target.

If you fall within the armed citizens’ standard deviation, your timing will be between 1.5 and 2.0 seconds.

Watch This Video

Now watch the following video.

Even a slow, short-legged, middle-aged female can cover 21 feet in 1.5 to 2.0 seconds.

How Close Should You Let an Attacker Get Before Shooting?

  • If you are unusually fast and accurate on the draw, and your attacker is slow, you might survive with a few cuts and bruises if you wait until the attacker is 15 feet away before shooting.
  • If you are slower or less accurate than average, and your attacker is a fit young man, he may easily stab you to death from a standing start 30 feet away.
  • If you and your attacker are both within the normal range, then you may be killed if you let a knife-armed threat get within 21 feet.

Explaining Tueller in Court

The public does not realize that a knife is a lethal threat beyond arms length. Consequently, if in self-defense you shoot a knife-armed attacker who was beyond arms length, you will probably be charged and prosecuted. You must then persuade the judge (to allow the testimony) and jury (to accept Tueller’s findings) that the attacker really had the opportunity (as well as ability and intent) to kill you.

If the judge allows the testimony of expert witnesses, then explaining Tueller in court become straightforward. Many internationally known and respected firearms instructors are available to testify as to the accuracy and validity of Tueller’s results. They are not normally available for free, but The Armed Citizens Legal Defense Network provides expert witnesses (including Dennis Tueller himself) at no cost to members.

You Must Prove That You Already Knew

On the other hand, many judges do not allow expert witnesses to testify in self-defense cases. They argue that the issue is not whether experts agree that a knife-armed attacker 21 feet away can kill you. The issue before the court is whether you knew this fact. You are the one who shot the attacker, after all. You must prove to the court’s satisfaction that you already knew the Tueller Principle, long before the self-defense incident. If you cannot prove that you knew beforehand, then you cannot claim that you were in fear for your life.

Most instructors recommend that you keep an audit trail of your training:

  1. When you learn the Tueller Principle in class, write down your understanding in a dated, signed, set of notes.
  2. Mail the notes to yourself in a sealed envelope.
  3. When the letter to yourself arrives, do not open the envelope. Instead, put it away somewhere safe.

The postmark date on the still-sealed envelope will be accepted as evidence that you already knew the Tueller Principle, that you knew you were in mortal danger when you fired.

As an alternative, I suggest that you simply post a comment to this essay. Your comment need say nothing beyond “hello”. The point is that today’s date, time, your IP address, and your username will be permanently recorded in the blog database. The blog comment itself will serve as permanent evidence that you knew the Tueller Principle as of today (the day that you posted the comment).

Next Time: Ability + Opportunity + Intent


Frank W. Sweet is an NRA-certified firearms instructor who teaches the safe and effective use of handguns for self-defense. He was awarded an M.A. in Civil War Studies in military history from American Military University in 2001. He is the author of Legal History of the Color Line (ISBN 9780939479238), Six Gems of Forgotten Civil War History (ISBN 9780939479023), and of numerous published historical essays. To receive a schedule of his firearms training courses, email to The information above should not be construed as legal advice.

16 Responses to “The Tueller Principle”

  1. Princess Says:

    Most intelligent women shloud learn a basic self defense strategy.Avoid potentially aggresive people who may harm you: whether male or female.Don’t attempt to be friends with a violent or emotionally unstable person.And never into an argument with someone physically larger than yourself.If someone who is larger than yourself uses entrapment or verbal commands to force you to do something, against your wishes, ignore them or leave a difficult relationship as soon as possible.

  2. Frank W Sweet Says:

    I agree wholeheartedly. Women are vulnerable to predators. I recommend that every adult female carry a pistol for self-defense. Where this is impossible, as in the UK, cautious awareness is essential. In this light I urge everyone, but especially women, to read Gavin De Becker, _The Gift of Fear_.

  3. David Molter Says:

    Interesting findings. Thanks

  4. Caylen Craven Says:

    Hopefully I’ll never need this, but if I ever do now I know

  5. Tim Says:

    Good information

  6. Test Says:

    Great blog post thanks for posting

  7. Ty Says:

    That’s cool

  8. Robert D. Says:

    Good post.

  9. Brad cook Says:

    Great post!

  10. Joe McFarland Says:

    Thanks for the info and the reminder.

  11. Anthony Says:

    Good information, Thanks!

  12. Louis Says:

    Thanks for the great information!

  13. David S. Bloch Says:

    Really interesting — and important — result. Thanks for posting it.

  14. Reinhard Schwaninger Says:

    Thank you, I hope I’ll never be in that situation!

  15. Evan McCuistion Says:

    Very intelligent advice given on this website. I hope hundreds of thousands are reading.

  16. Howard Grund-Clampit Says:

    Thank you for posting this information.