What is the Arrow Spine

Have you heard of this confusing term? You are probably overwhelmed by all the information available on the subject. The deeper you dig about arrows, the less you seem to know but don’t worry, even if it is good and interesting to know about the science behind the arrow, you don’t need to know it all, especially if you are at your beginning stage as an archer. Most of the work was done by other people before us so we don’t need to reinvent the wheel. After all, this is exactly why spine charts now exist for us to use.

By the end of this post you will not only know what is the arrow spine and how it can affect your shooting but you will be able to point the right one to choose from that best suits your needs without falling into common mistakes, such as choosing too weak of an arrow for instance (under spined). I will break it down to simplify the understanding and everything will suddenly become a lot clearer.

I won’t throw too much scientific terms and descriptions your way, I will briefly oversee kinetic energy and momentum so you get the idea of what it is and how it can impact a bow hunt by showing a real life example without falling into endless calculations.


The Basics

Basically, the smaller the number, the stiffer the arrow. The reason is simple when shot, the arrow bends sideways like the movement of a snake. So if the arrow is very stiff, it won’t flex as much as a weak arrow.  

The deflection of an arrow, represented in inches, is determined at a fixed length and under a fixed amount of weight.


Arrow Spine


A very stiff arrow might only bend 0.300 inches. Some manufacturers take this number and multiply by 1000 and get that 300 spine number. Although, note that not all manufacturers use the same method to determined spine numbers so do not let yourself think that a 300 arrow spine for one brand is necessarily the same for another brand. Each one has their own charts and with the following info included in the next paragraphs, you will be able to navigate in those charts in seek of the proper arrow spine number that is just right for you no matter the brand. Simple right!?


How to Determine the Arrow Spine

Here are three important values you need to determine the spine of the arrows you should be using:

  • The Draw Weight
  • The Arrow Length (usually 1 or 2” longer than your draw length)
  • The Point weight

When you know those three values, you will be able to look up into manufacturer’s charts to find the ideal spine number you need. Let’s have a more in-depth look to each of those values:


- The Draw Weight

The more weight pushes the arrow, the more it will flex. Knowing the peak draw weight you are shooting with is important and must be measured with a bow scale. A few pounds can make a difference for the spine you should be using. When I say peak draw weight, it does not necessarily mean the maximal poundage of the bow, it is the poundage you are shooting with at full draw which needs to be measured with a bow scale for more exactitude. Even if the bow is said to be a 70 pounds, it would be possible that the real draw weight to your own draw length is in fact 67 pounds, which can have an incidence when looking up the spine chart. Do not try to shoot with a high poundage straight from the beginning, gain some experience with a lower draw weight first. If you are uncertain of the draw weight you should start with, read one of our previous blog post on How to Determine Draw Weight.


- The Arrow Length

The longer the arrow, the more it will flex. The arrow is measured from the end of the nock at the bottom of the opening where the string rest at the end of the shaft, excluding any points or broadheads. The length of your arrows should be between 1 or 2 inches longer than your actual draw length. If you don’t know what your draw length is, let’s find out with this previous post on How to Measure Draw Length.


Arrow Length


- The Point Weight

The more weight at the extremity of the arrow, the more it will flex. An 85 grains field point won’t bend the arrow as much a 125 grains would so be sure to know what you will be using. If you plan on shooting on a target with field points and go for a hunt with broadheads, later on, try choosing the same grain for your points and the broadheads you will be using to be sure you will stay properly spined. 

Now I know what you are thinking. Cut the theory and show me some charts! So here you go…



Arrow Spine vs Arrow Weight

Do not confuse Arrow Spine and Arrow Weight. The spine represents the stiffness and has nothing to do with the weight of the arrow. If you choose one arrow with a certain spine, although affecting the flexibility, it will remain the same spine number when cut to match your draw length needs whether it is 28” or 30” but the weight will inevitably be affected when cutting out a part of the arrow. Same spined arrows of different models will most likely have different weights, so if you want to shoot lighter arrows to increase speed, look for a change in weight not in spine. Spine means stiffness, nothing else. More on arrow weight later on.


Don’t go cheap

Once you have determined the spine you should use, please do yourself a favor and don’t go cheap on arrows. If you have purchased a nice piece of bow, don’t screw its potential by selecting low-quality arrows. It does not mean that you need to pay hundreds of dollars for a single pack of arrows but you need to “target” quality ones. You wanna group those arrows!? Then you need to take on quality.


Under Spined Arrows

This issue is frequent. An under spined arrow is a week arrow and as I said, a weak arrow gets more flex. More flex means that an arrow propelled with too much force for what it has been designed for will bend more so the “snake” movement will be exaggerated when it flies and will keep on going. Therefore taking too much time to recover and not becoming as straight as it should, causing inconsistency when it hits the target.


Over Spined Arrows

This issue is not seen very often. Being over spined could mostly occur when using low draw weight recurve bows. Opting for a lower poundage bow would prefer arrows with more flexibility (deflection). When shooting off the shelf, the arrow would hit the riser in a certain way that requires a certain amount of flexibility at a certain amount of force. Too stiff, the arrow won’t bend enough, therefore causing improper arrow flight and lack of accuracy. On the other hand, today’s compound bows can hardly be over spined, deploying aggressive force very efficiently that prefers stiff arrows.


Other Factors

If you are shooting with proper spined arrows, know that there are many other factors that might affect the consistency of your accuracy. Your general archery form for instance and your release technique are some of them.

The material of the arrow shaft is also responsible for consistency. Wooden arrows are especially used by traditional archers and do not offer close as much options as the modern arrow does. Aluminum shafts are renowned for their straightness. Carbon shafts offer a lot of options for straightness and diameter while having a lot less glare. The size of the shaft can be influenced by climate, a windy day would have a greater impact on larger diameter arrows because of the higher friction.

Those are a few factors and much more are possible so if your accuracy is not optimal, it can be caused by something else than the spine of your arrows.


Kinetic Energy & Momentum

Both, kinetic energy and momentum are affected by the same two factors within different equations, arrow weight and arrow speed. Think of it this way, kinetic energy favors speed while momentum favors heavier arrows (penetration potential). Picture a light race car (light projectile) going towards a concrete wall (target) at 100 mph and a school bus (heavy projectile) going towards the same wall at 50 mph. Which one would have greater penetration? In other words, which one would be easier to stop? Maybe something in between like a large heavy SUV at 75 mph would be harder to stop. Even if much exaggerated in the example, choosing an arrow is about the same way to look at it, especially for bow hunting. If you target a large tough game and you hit the shoulder bone, will your light and fast arrow have enough penetration to put it down or will you be in favor of a slower yet heavier arrow?

Try our Kinetic Energy and Momentum Calculator.


Real Life Example

Now we have seen a lot of information so I will use a real life example to put you in context and wrap everything up in the meantime. I will use average metrics of an individual going for a moose bow hunt.

  • Draw Length = 28”
  • Arrow Length  = 29”
  • Draw weight = 70 lbs
  • Point weight = 125 gr.

For the purpose of the example, I will use Gold Tip Camo Hunter XT Arrows and with the values above, I will seek the spine within the chart I have shown you previously. It gives me a spine of 300.

Great! I am all set with the spine. Now, do I have enough power to put down a moose? I know that the arrow I have selected along with the value of the spine weighs 10.9 gr./in as per the specs of the manufacturer. So 10.9 gr./in. X 29” (arrow length) = 316.1 gr. So my arrow shaft alone weighs a total of 316.1 gr. I must add my 125 gr. broadhead, my 24.2 gr. Inserts (2), my 11.5 gr. nock and my 7 gr. vanes (3) to that value which brings the total weight of my arrow to 483.8 gr.

Let’s assume that I am shooting those arrows at a minimum speed of 260 fps (You may be interested in reading more about IBO Speed). Now let’s enter those two values (arrow weight and arrow speed) into the Kinetic Energy and Momentum Calculator ...This shows me that this setup will result in a bit under 73 foot-pounds per second of KE. If I am shooting at a distance of 30 yards, I would lose approximately 2 ft-lbs per 10 yards, therefore my KE would be a bit over 66 ft-lbs once reaching the game which is slightly over the acceptable limit of the kinetic energy requirement for that kind of game.

One lesson you can retain from that example is that, although important, speed isn’t everything. A lot of people are crazy about speed but momentum is also a thing often overlook or not considered at all. Not all bow are the same even set at the same draw weight and might not shoot arrows at over 300 fps like some bowhunters would absolutely look for.

As you saw in the example above, I had a bow shooting hunting arrows at 260 fps and was powerful enough to hunt any big game because of the arrow I used which increased not only kinetic energy but also momentum which favors penetration. If I had used a lighter arrow, like a 350 grains, I would see my speed increase (about 1 foot per second for every 4 grains I subtract) to around 293 fps but be giving me a kinetic energy value of a little bit under 67 ft-lbs, minus the velocity loss over 30 yards, I would stand at a bit under 61 ft-lbs per sec of KE. This would be a major impact on the hunting capability of the bow and would not be recommended for toughest games anymore. Momentum is also greatly affected by the weight change of the arrow, reducing its penetration potential.

Play with the calculator and look at the impact on both kinetic energy and momentum as you change the weight and the speed of the arrow. Also note that the more speed you have, the more noise the arrow will make. The idea is to find the sweet spot you are comfortable with by keeping in mind that a lighter projectile will favor speed while a heavier one will favor penetration.



To conclude, choosing the proper arrow spine is important to develop an optimal consistency and tighten your groupings. We saw that you needed three values to select the spine required, the draw weight, the arrow length and the point weight.

We also oversee some of many factors that can be at the origin of discrepancies and inconsistencies in your shooting such as the arrow material, the size of the shaft and even other factors like your archery form or your release technique.

We followed with a short explanation of kinetic energy and momentum which brought us to a real life example in a bow hunting situation to see concrete impacts on what can be hunted under a certain arrow weight and speed after selecting the optimal arrow spine.

Now you have pretty much all the information you need to know to make a clear selection of what you need and other than the arrow spine, keep in mind that some setup can work well for an archer and not so much for another.

Basically, there are some general recommendation guidelines but there is no truth science, it all comes down to personal preferences and what you are comfortable with.

Hope that you found value in this post! Feel free to share and comment!

Thank you for reading!




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