Are you wondering how to determine the draw length you need for bowhunting? Check out our draw length calculator below to easily and quickly determine it!
Draw Length Calculator
Wingspan (take a measurement of your wingspan between the fingertips of your middle fingers)
move slider or enter value
inches
Draw Length:
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What is draw length?
With traditional bows, you can basically pull back as far as you are able, based on the draw weight of that particular bow. The same is true for a recurve bow.
Draw length is an extremely important component to good form and repeatable shot mechanics.
However, you will typically find that draw length is discussed in regards to compound bows. This is because a compound bow has a set maximum draw length, once you hit the “back wall” of the draw cycle (the back wall is the place in the draw cycle where you can no longer pull the bow any farther.)
If you don’t want to use the N1 Outdoors draw length calculator above and instead want to figure your estimated draw length with good ‘ole mathematics, the first thing you need to do is measure your armspan (or wingspan).
Spread out
First you need to determine your armspan. Simply spread out your arms (don’t over-stretch) with your palms facing forward.
Measure
Measure the distance from the tip of one middle finger to the tip of the other middle finger.
Do some old school calculating
Take the measurement from step 2 and divide it by 2.5. This will provide you with a fairly reliable estimate of your appropriate draw length. Check with your local bow shop to help you fine tune.
Here’s what the Archery Manufacturer’s and Mechants Organization (now the Archery Trade Association) says about draw length:
“Draw length is a specified distance, or the distance at the archer’s full draw, from the nocking point on the string to the pivot point of the bow grip (or the theoretical vertical projection of a tangency line to the pivot point parallel to the string) plus 1 3/4”. Draw length from pivot point shall be designed at DLPP and shall be called TRUE DRAW LENGTH. EXAMPLE: 26 1/4” DLPP plus 1 3/4” is the equivalent of 28” draw”
AMO Standards Committee FIELD PUBLICATION FP-3, 2000
So, by this definition, if you have a “28-inch draw length”, that means that at full draw the distance from the deepest point of the grip to the nocking point of the string would be 26.25 inches.
It’s important not to confuse draw length with arrow length. While they may be similar lengths, they are measured differently.
Arrow length is measured from the front end of the arrow shaft (not including the broadhead or field point) to the throat of the nock.
Your arrow length can vary depending on what you are trying to achieve regarding the FOC and spine of your arrow. (Spine is how much your arrow flexes at a set length with a set weight attached. More on arrow spine here.)
Arrow length is the measurement from the end of the arrow shaft to the throat, or groove, of the arrow’s nock.
When it comes to archery and bowhunting in regards to compound bows, “full draw” is when you have reached the farthest point that the bow can go in the draw cycle, reaching your anchor point.
What is an “anchor point?”
The “anchor point” is a reference point for an archer or bowhunting that they can “anchor” the bow string or the shooting hand when they are at full draw.
An anchor point helps make the archer’s shot repeatable, so that shot consistency can be achieved.
For example, many bowhunters will anchor the knuckle of their index finger just below their ear lobe behind the jaw.
Others may use a “kisser button,” (of all the parts on a bow, this might be the most memorable) which is usually a small disc that is installed on the bow string, above the nocking point.
Many bowhunters will use an anchor point just below the ear, resting the knuckle of the index finger in the area right behind the jaw.
As you can see, draw length measurement is a critical part of becoming a good archer. We hope this article and our draw length calculator has been helpful to you!
When it comes to archery, IBO stands for International Bowhunters Organization.
What is IBO Speed and how is it calculated?
You might have seen where compound bows have an IBO rating.
But, what does that really mean?
Well, the IBO speed of a bow is calculated using a bow with a draw weight of 70 lbs, a draw length of 30 inches, and an arrow weight of 5 grains per pound of draw weight. So, that would mean a 70-lb draw weight would be shooting an arrow that weighs 350 grains (70 x 5 = 350).
That arrow is then shot through that bow through a chronograph, which measures the arrow speed. The average speed becomes known as the IBO rating of that particular bow.
The problem with IBO ratings, however, is that they are not typical of most hunters’ setups.
For example, a 30-inch draw length is rather long for the average archer. Also, an arrow weight of 350 grains is simply not typical of most hunting setups. And, with high FOC arrows gaining popularity, the arrow’s grains per inch is often significantly greater.
So, when using the arrow speed calculator above, you must understand that the IBO rating you enter is based on this premise. The calculator will give you an estimate of how changing the inputs that make up IBO could affect your arrow speed.
The arrow speed calculator makes the following assumptions:
Every inch of draw length under 30″ will subtract 10 ft per second from the IBO value.
Every inch of draw length above 30″ will add 10 feet per second to the IBO value.
Every 3 grains of total arrow weight above draw weight multiplied by 5, will subtract 1 foot per second from the IBO value.
Every 3 grains of additional weight on the bow string will subtract 1 foot per second from the IBO value.
The arrow weight in grains (includes fletchings, wraps, inserts and also points/broadheads
Total string accessory weights in grains (peep, tube, silencers, etc.). For your reference, an estimated peep only weight is 20 grains, and a peep + tube is 45 total grains.
When it comes to your bowhunting setup, knowing the “Kinetic Energy” of your arrow allows you to know how much energy that arrow possesses due to motion, from being shot by your bow.The “Momentum” tells youhow much force it will take to stop your arrow when it reaches its intended target.
Kinetic Energy and Momentum Arrow Calculator
Kinetic Energy and Momentum Calculator
Arrow weight Value must be between 250 and 1000 grains.
move slider or enter value
grains
Arrow speed Value must be between 100 and 500 Feet Per Second.
move slider or enter value
fps
Kinetic Energy:
0
Momentum:
0
If you know your arrow’s weight (in grains) and your arrow’s speed (Feet Per Second), then you can use our Kinetic Energy and Momentum calculator above to find out each! Simply move the sliders or enter the values in the blanks. And, if you really want to take a deep dive into the Kinetic Energy of arrows, check out what the Ranch Fairy is up to below…
Kinetic Energy And Bowhunting (How I Got Here)
As you may already know, the ‘ole Ranch Fairy (that’s me) is quite out of the norm in his measuring of arrow systems. (If you aren’t aware, I am definitely one of the strange ones in the bowhunting world.)
In all fairness, I have been heavily influenced by Dr. Ed Ashby’s 12 Arrow Penetration Factors and his almost 30 years-long Natal Study. These are, in fact, the basis for my YouTube channel and all of the research I have been doing therein.
Anyway, just to set the record straight, the biggest overlap between Dr. Ed, the Ashby Bowhunting Foundation, and the Ranch Fairy is simple: We want to know the highest performing projectile for all impact points to pass through the animal you are hunting.
I like to put it this way: Archery is shooting a target… bowhunting begins at impact with the target.
Finally, I am constantly seeking higher performance and am always questioning what I know today.
Why?
Because the longer I live, the more I look back and say, “wow, my assumption about bowhunting 3 years ago (along with many things in life, not just bowhunting) was flawed.”
I keep learning because I kept asking “why” and kept trying to find out ”why.”
I like to say, “It’s better to have smart friends than to be smart.” And, I have had the luxury of meeting ‘Big Mike’ who has coached me on the “functional bow and arrow flight” part of this game.
And then, the latest addition… enter, “The Rocketman,” Darrel R. Barnette.
Darrel spent 30 years with the Department of Defense (D.O.D.) testing “boring” things like, tank penetrators and rail guns.
Just to clarify, the Rocketman says he technically never worked on a ‘rocket’. But, he did shoot, test, and evaluate hard target penetrators pushing Mach 11.
So, ya know, an arrow is a bit slower.
Here’s the Rocketman “aiming’ what is known as a lab radar.NOTE: (If you have a bowhunting idea or concept, Darrel does testing and you can reach him at d_barnette@digtodef.com.)
Heretofore, Darrel is known as “the Rocketman.”
When the Rocketman starts talking, he gives me about 15-20 minutes (until steam starts to come out of my ears) and then he pulls back on the reigns.
Ballistic coefficient, Poncelet equation, yaw, lift, aerodynamic friction and drag, the Physics Hyper Textbook on and on and on.
The first time Rocketman said, “well, Troy, a bow is just a spring with fixed Kinetic Energy,” I thought… BLASPHEMY!
But, from what I understand, he is right.
The bow can’t “make” more KE. It is what it is.
BUT, you can change the arrow and gain some…..so hang on. Let me set the table here…
A bow is just a spring with a fixed Kinetic Energy. It can’t make more kinetic energy than what it already possesses.
KE Arrow Testing
On a basic level, radar measures a projectile’s speed over distance.
The testing unit that we used measures 5 total distances. So, if you want to shoot 60 yards, the computer divides that distance into 5 increments.
[NOTE TO SELF – you need to put the target further than 60 yards to capture the flight speed. To address this, we placed the target at 70 yards. Because, if impact is at 60 yards, the data would be flawed for velocity testing because the target stops the arrow at a yardage that it should be being measured.]
Below is the spreadsheet, graphs, etc., shooting 3 different bows under the conditions described above.
Yeah, its super small. I don’t intend for you to read it and geek out (but that’s coming… keep reading!)
Just know that it’s a lot of information, and we ran the best test we know to do… today anyway. (See my comments on being smart, today, included earlier in the article. We will be smarter very soon!)
The Tools In Our Kinetic Energy Toolkit
The three bows we used in the Kinetic Energy testing were:
The top line is the launch velocity. The change in velocity is super boring… Until you look at the 60 yard impact KE.
The gap in the data sets shows the significant reduction in KE over distance. However, you see that gap narrow as arrow mass increases.
As you can see, in all the above graphs, the launch KE is relatively constant, but alas, further away, at 60 yards, with higher mass projectiles, we see something worth pondering. (Well, only if you think math is correct!)
What are the results telling us? (Please pardon the steam coming out of my ears)
So, despite my heavy arrow bias, (I’m not much of a hair splitter), increasing launch KE 3-6 ft/pounds is really boring.
But the lower line, at 60 yards, is worth chewing on.
If you search around, many of the wide mechanical broadheads suggest KE’s of 45-60 ft-lb’s. Now, they don’t go out on a limb and say, “that will create a pass through, or break bones.” It’s just a recommended impact KE.
Formula for Kinetic Energy: K.E. = 1/2mv2 (where m=mass of object and v=velocity)
And be clear, just like the firearms world, this is launch KE, maximum velocity. This is because a projectile can’t go faster once it leaves the muzzle or the string… It’s always slowing down.
Silly aerodynamic drag.
Now in a vacuum… oh wow, throw in some zero gravity and guess what?
It still doesn’t go faster….. it would maintain launch velocity and you wouldn’t be able to breathe to test it.
Some adult field points and some, ahem, “super weenie points.”
There have been multiple companies and YouTube personalities showing fixed blade vs. mechanical pressure testing on deer thoraxes and other items simulating a critter. They use very complicated mechanical devices down to something as simple as a bathroom scale.
Let’s just say, the HUGE differences are eye popping.
It’s not half a pound or 3, it’s exponential. The “precision” of the device doesn’t matter when the difference is 40 pounds. Please search those tests up, because I know you’ll go do it anyway.
When it comes to arrow penetration, harder things push back harder… you can just blame Sir Isaac Newton for that and keep my hate mail down!
If X brand broadhead requires 50 ft-lbs to penetrate and another type takes, say, 10 ft-lbs., which one leaves you more energy to continue pushing?
Remember Newton’s 3rd law…“For every action there is an equal and opposite reaction.”
So in this case, the tissue will push back 50 ft-lb on the one broadhead and 10 ft-lb on the other… but the arrow is exerting 70 ft-lb.
Given that, the broadhead requiring 50 ft-lbs has to have at least 50.1 ft-lbs. to continue moving and the 10 ft-lb broadhead requires 10.1 ft-lbs to keep moving.
The arrow has to overcome the equal and opposite push back exerted by the tissues: hair, meat, bone, etc.
If you can shoot between the ribs every single time, none of this matters. I’m not that good, so give me the heavy stuff!
PLUS, here’s the kicker. Harder things push back… harder.
You can just blame this on Newton’s 3rd law of physics. This will keep my hate mail down!
So, for the 50 ft-lb broadhead, if your bow produces 70 ft-lbs, you have 20 foot pounds of extra work potential.
Now, with that same bow generating 70 ft-lbs, shooting a beefier broadhead that only requires 10 ft-lbs to penetrate, has 60 ft-lbs of extra work potential.
If you could guarantee you’d never hit anything hard on a deer, elk or other critter, and always shoot between the ribs, none of this matters… you have a winner.
I’m not that good. So, give me all the extra I can get!
What we haven’t studied, is actually shooting the different broadhead platforms to measure the exit velocities or impact velocity. That one will take “some doing” to get it right.
Trust me, I want to know if I am right and “why.” The math here says I am. But Dr. Ed always says, “we won’t know until we actually test it under those conditions”.
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