Kustom King Spine Calculator

Arrow Length

• We measure from the valley of the nock to the end of the shaft 

Grains Per Pound

• In most cases the GPP of your finished arrows should be around 8 GPP
• Arrows have a GPI or grains per inch
• Example:
  • 40@28 Bow
  • Minimum of 320 grains total arrow weight (all components)
  • 29" 500 Spine Arrow with 8.3 GPI
  • 125 Grain Point
  • 370 Grains total weight

HOW TO FIND THE SPINE

• A Spine Selection Chart (page 2) is a great starting point in finding the correct spine on an arrow. Though that doesn’t make it an exact match for your bow and your personal preferences. That’s why this is all custom, make the archery equipment that best fits you.

STEP 1: FIND YOUR ARROW LENGTH AND DRAW LENGTH

• Finding the correct Arrow Length by drawing back an extra-long arrow to a full draw while having a helper mark the arrow just in front of the handle. Then measure that mark to the deepest part of the nock groove. That is your Draw Length. It is recommended to add 1–2 inches to this measurement so the broadhead doesn’t bump into the bow. Not as necessary for target archery but still need to measure to make sure the arrow doesn’t come off inside the bow shelf.

STEP 2: DETERMINING ACTUAL PEAK BOW WEIGHT

• This is measured while determining your draw length, not by what is written on the bow. The bow will be about 2–3lbs different for every inch of the rated draw length. The industry standard is for bow manufacturers to be +/-2lbs from the rated bow rate. So this could change your bow rating up or down. So using an accurate scale, draw the string until you hit your draw length and hold. Record the weight on the scale, even repeat a few times to make sure you have an accurate reading.

ARROW SELECTION CHART

• Once you have the Arrow Length and Actual Bow Peak Weight recorded, you are ready to select your correct arrow spine by using the chart on the next page. find your bow type and weight, as well as the point weight you will be using. Move across the chart until you find your arrow length, and there you go. Though remember, these are only recommendations and through testing, you will find what works best for you.