Muzzle Energy Calculator

My favorite Muzzle Energy Calculator was hosted by AirHog, makers of high quality air gun tanks, valves and other accessories. Airhog redesigned their website a while back and have taken the old site offline, which included the calculator. Through the magic of the Internet Archive, I have resurrected and improved their calculator. Hopefully they will not mind, I have emailed them asking for permission. If anyone is interested, my improved javascript code for the calculator is here.

First choose the system of units, either English Units (also called United States customary units, Traditional units or Imperial units) if you are in the USA or Metric if you are in Europe. The rest of the world uses one or the other depending on how manufacturers have decided to market their products.

Then enter two of the three variables (weight, velocity and energy) and hit Calculate. The system will calculate the third variable which you did not enter.

Muzzle Energy Calculator

English Metric
 ft/s  m/s
Pellet Weight:
 grains  g
Muzzle Energy:
 ft-lbs.  joules


Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • ARCNA442

    I noticed that the calculator converts units after calculating. Would it be possible to do this before calculating so that the user can input one metric and one imperial value? Sometimes information is given in a mix of units (such as bullet weight in grains and velocity in meters per second) and it would be nice to not need an additional converter.

    • garlic_b

      Even better, make it live updating, where as you change one value, all other values are updated.

  • Darryl

    That is quite the formula. I was taught an easier one which is….velocity squared X bullet weight and divide that by 450,240.

  • Always good to have more resources available.

    Having said that, it’s super easy and requires only a little memorization to do muzzle energy calculations with your phone calculator. In my case, I find it’s easier to convert English units to metric and do it that way than it is to actually remember and add in the conversion factors necessary to do the English math. And, of course, my way, if you encounter metric units in the field you’re not up a creek.

    Here’s an example, with screencaps from my Android phone;

    Find the energy in Joules and ft-lbs of a 155gr projectile moving at 2,800 ft/s.

    First, take the velocity in ft/s, and divide by 3.28 to convert to meters:

    Now, take the result and square it:

    Take that result, and multiply it by .5:

    And then multiply it by the weight in grains:

    And divide that result by 15,432, to get the result in Joules:

    If you want a result in ft-lbs, simply multiply by .738:

    This method is designed for use on a simple phone calculator, as long as it can square figures. Hope it helps!

  • guest

    1000 m/s
    10 g
    = 5000 J

    3330 ft/s
    154.32 gr
    = 3688.404 ft/lbs

    The sooner the imperical system dissapears the better.

    • I rather like the empirical system. 😉

      • gunslinger

        at my job i fought tooth/nail to keep US measurements. most of our products come from France or German. and of cousre all drawings are in metric.

        now i do metric drawings and love it. much easier to add dimensions (what’s 2′ 3 and 3/16 plus 1 7 and 9/32′? shit let me get my slide rule. what’s 150.73mm plus 248.15mm?)

        granted if we did 2.75 feet it’d be the same but we don’t have any decimal tape measures here.

        • I was making a joke at the confusion between the words “empirical” and “imperial”. The Imperial system is the standard in the US, but that’s one of only a handful of reasons to like it. The metric system is quite a bit better.

    • big daddy

      I agree, I cannot believe we still us it in the USA. They started teaching the metric system to us in school and stopped that was 50 years ago. I had to learn it again in the Army. It’s not that hard to adjust, but the American public will not and the powers that be think the American public is too stupid, maybe they are. After reading comments on web sites it makes me think as a whole on average the American public is pretty ignorant and uneducated.

      • Giolli Joker

        One thing that I love of the internet arguments between metric and imperial supporters is that the latter ones always end up pointing out that the US set foot on the Moon by doing the calculations with the imperial system…
        Very true, but quite funny to notice that NASA is one of the first American institutions to have switched to the metric system.
        Anything works, but the metric system is without doubt more rational and easier.

      • dp

        Those are harsh word at the end by I concur with your view. Maybe there is intention right from top to keep it that way.
        At the same time, form my own experience, I worked for a company in States which made products in both systems. So people are able to adopt and to learn.

      • The only way to do it is by legislating metric as the only acceptable “official” standard, and refusing to use the old Anglo-American (they really aren’t “Imperial” units, actually. . . the American system is from the PRE-Imperial British system. . . ) units for official purposes.

        That is *literally* the only way to successfully wean a non-metric society off their non-standard units. Otherwise, the BEST you get is someone like me, who uses mixed measurements as needed on a case by case basis.

        As a consequence of growing up “anglo-American” units, but serving in the Army:

        I drive (both distance and velocity) and run in “miles”, measure height and weight of humans in feet, inches, and pounds. Temperatures are in fahrenheit. Fluids other than water are in gallons and pints. ALL kitchen measurements are in standard American units. If I need to “cross units”, I have to stop and deliberately convert in my head.

        But I WALK in kilometers, measure distances beyond “room size” in meters, shoot in meters, measure water in liters, weigh things I have to carry in kilograms, measure things less than human height in mm, cm, and meters, (except my “eyes” can still readily wrk in inches up to about a foot and a half), etc. Again, I would have to deliberately convert in my head to translate if switching units.

    • Martin Grønsdal

      a cube with 10 cm long sides is 1000 square cm, or a liter, if filled with water it weighs one kilogram, freezes at 0 degrees Celsius, boils at 100 degrees. Make a thousand of these cubes filled with water, and you have a ton. And that ton fits a cube with a meter long sides….

      • dp

        You are right – 1000cc of water weighs 1kg (at g = 9.81m/s^2), but there is a caveat. It applies between 22.5-23.5 deg. C. Also, to obtain/ lose 1cal (calorie) you need to warm up same amount of water in that range. But, overall, metric is simple to use. Quarter of Earth’s circumference ant 45deg latitude is 10,000m…..

        • Martin Grønsdal

          When it boils down to real use, it is like red cars or blue cars. It doesn’t matter. ..

    • dp

      Ah common; its cute. It is artificial preserve of times gone by – history. I do not have problem with most of it (dislike BTUs and deg. F), but yes it is awkward especially for foreigners.

    • ARCNA442

      I used to think that way, and for science you’re probably right, but in the everyday world the Imperial system is far better.

      All the measurements are in human terms – think about giving someone’s height in feet/inches versus meters/centimeters or trying to estimate weights in grams. The metric measurements offer standard units that are simply too small for casual use.

      This also assists with making measurements in our daily lives. Sure, it won’t do for building a rocket, but when you need to know how much carpet to buy, knowing that a foot is roughly the length of a real foot is quite helpful.

      Finally, while base ten is nice for conversions, base sixteen has the advantage of being easily divisible without using large decimals.

      • This is the stupidest shit I’ve heard all week. The only real reason to prefer one system over another is to avoid the work of learning the other.

        “All the measurements are in human terms – think about giving someone’s
        height in feet/inches versus meters/centimeters or trying to estimate
        weights in grams.”
        >>The relationship between inch and feet is similar to the relationship between cm and m… except the conversion is easier.

        “The metric measurements offer standard units that are
        simply too small for casual use.”
        >>Do you want a chance to rewrite this?

        “when you need to know how much carpet to buy, knowing that a foot is roughly the length of a real foot is quite helpful.”
        >>When you buy carpet, do you walk toe-to-heel across the room and go buy based on that, or do you grab the nearest tape-measure and use that?

        “Finally, while base ten is nice for conversions, base sixteen has the
        advantage of being easily divisible without using large decimals.”
        >>I would be grateful if you could check out the tables on this Wiki page ( and tell me where on earth base 16 comes in to play anywhere in this conversation.

      • gunslinger

        Mr. Arcna442, what you’ve just said is one of the most
        insanely idiotic things I have ever heard. At no point in your rambling,
        incoherent response were you even close to anything that could be considered a rational thought. Everyone in this room is now dumber for having listened to
        it. I award you no points, and may God have mercy on your soul.

      • guest

        Oh, so you can relate for example a “stone”, a “furlong”, a “chain” or a “furlong” or “yard” to human terms?
        I can of course see what you mean and I say this with sarcasm in mind, but arguing for having a backwards system where one unit of measurement is incompatible to another is stupid.
        The entire metric system revolves around water at 4 degrees Celsius, and every unit is either a multiplied or divided result of something by a factor of 10, 100 etc. If at least there would be sense in the imperial system (if 1 foot was 10 inches, one yard 10 feet, one mile 1000 yards etc) that would make sense.
        But calculating for guns using mph for wind, yards for distance, grains for weight, feet for drop and foot-punds for energy is retarded. Neither one of these units is compatible with the next. And using fractions is the most retarded way of doing things: a fraction is literally a FORMULA not a unit! 1/4 or 3/16 of ANYTHING does not exist in nature! There are only wholes! And the only reason anyone would use fractions is to shorten an endless result (like 1/3= 0,3333333333…. ad infinitum).
        The stupidity of this system is further illustrated by the incompatibility of units: a british gallon is not the same volume as US gallon, there’s a ton and a short ton etc. No wonder people get lost in this system.
        But a meter in France is a meter in Japan.

        • gunslinger

          1 stone is 14 pounds!
          actually, i think the brits use stone for weight.

      • Humans run the gamut in terms of body size. It doesn’t seem reasonable to me to assume that more people would be able to correlate a yard to a part of their anatomy than a meter, for instance, or even a centimeter vs. an inch.

        Here, I will demonstrate: A centimeter is approximately the width of the nail on my index finger (which is a nice, rigid body part that’s good for measuring!). A meter is about five of my handspans, or about the distance from the end of my outstretched hand to my opposite shoulder. A kilogram is about two pounds, so if you can estimate a person’s weight in pounds, it’s no more difficult to do so in kilograms. Multiply by a thousand if you wish to know the weight in grams. Further, a gram is about the same as the weight of a paperclip.

        I would urge anyone who thinks in Imperial units and uses common body measurements to approximate the size of objects, to try to do the same for a month or so using only metric approximations, such as those described above. You might be surprised.

        Having said this, Imperial is clearly superior in the divisibility department. This is less important now than it once was, and comes as a packaged deal with being less well suited to base ten calculations (which is the whole point of metric), but the only way to solve this would be to move to base sixty. 🙁

        • ARCNA442

          I don’t doubt that people can estimate numbers in metric – I’ve done it myself on occasion. What I was trying to point out is that the Imperial system developed over hundreds of years to measure everyday objects by average people who usually lacked any real measuring tools. Thus, the most common Imperial measurements such as feet, inches, and pounds are quite intuitive in size.

          The metric system, on the other hand, was designed by scientists trying to construct a completely rational system and they succeeded admirably. This explains why scientists and engineers prefer the metric system even in America.

          In short, each system does some things well and is quite lacking in other areas. It is probably best to adopt the good parts of each in a hybrid system such as the US is using now rather than crusade for the eradication of one or the other.

          • gunslinger

            funny but i’m sure if you talked to any number of people who were brought up in the metric system would have no problem measuring every day object in metric.

            you ask a kid how long something is, they aren’t going to say about 3 lengths of my feet. they’ll respond with what they’re brought up with.

            i really wish we’d move to metric

        • ghost

          My finger nail is just right to hit with hammer. How far I throw the hammer depends on how hard I hit my finger nail.

        • guest

          We are scientifically way past the level of measuring anything with bodyparts. How about this; a rifle barrel is 5 dicks in length. Makes a lot of sense… not.
          And even feet are not feet, are everyone’s feet equal in size? This discussion is pointless.
          Metric system is mathematically simple, easy to learn and easy to use. Imperial is archaic and the arguments of keeping it is like people refusing to abandon horsewagons for trucks. The horse&bogy crowd will always have a “point”, but it will be like winning special olympics.

          • guest

            By the way in terms of people not being able to measure something because the metric system does not use body parts or whatever else: I know a guy who could measure metal sheet thickness by looking at it, down to 0,1mm precision, purely from experience. Your argument is invalid.

  • dp

    The formula is super easy, true.

    Now, you have energy at muzzle, good. Next: what to do with it? How far will that carry on down the range; with what loss? Will it strike the intended target and transfer in it? More practical is impulse-momentum, after all energy is a product of it.

  • ghost

    Metric means less tools, Combining metric with imperial = frustration. Evey thing almost fits, but not quite.

  • ghost

    I don’t go by metric/imperial, if it is close enough to shoot, shoot it.