What does the GPI mean to arrows

For archers, Arrow GPI stands for “Grains Per Inch” and is a crucial specification that describes the weight of an arrow shaft per inch of its length.

Here’s a breakdown of what it means and why it’s important.

What GPI Measures

The GPI value tells you the baseline weight of the raw arrow shaft material before any components (like points, inserts, fletchings, or nocks) are added. It is a standardized way for manufacturers to indicate shaft density and for archers to predict final arrow weight. GPI is almost always measured in grains, a small unit of weight commonly used in archery (1 grain ≈ 0.0648 grams).

For example, if an arrow shaft has a GPI of 9.6 and is cut to a length of 30 inches, the raw shaft’s weight would be approximately 288 grains (9.6 GPI × 30 inches).

GPI in Real-World Arrow Selection

When selecting arrows, you will often see GPI listed alongside other critical specs like spine (which measures stiffness). Here’s how GPI varies across different models:

Why GPI Matters to You

Knowing the GPI helps you make informed decisions about your setup:

1. Predicting Final Arrow Weight: By combining the shaft weight (GPI × length) with the weight of all components, you can calculate the total finished arrow weight (often called “grains total weight” or GTW). This total weight directly affects your arrow’s speed, kinetic energy, and trajectory.
2. Tuning Bow Performance: Heavier arrows (higher total grain weight) absorb more of your bow’s energy, resulting in quieter shots, deeper penetration (crucial for hunting), and less strain on the bow. Lighter arrows (lower total grain weight) fly faster and with a flatter trajectory.
3. Comparing Arrow Models: GPI allows you to compare the inherent weight of different shafts. A model with a GPI of 10.5 is inherently heavier and will create a heavier finished arrow than a model with a GPI of 7.2, even if they are the same length and spine.

How to Use Arrow GPI

To find the right arrows for your bow and purpose, you can combine GPI with two other key specifications:

• Spine: This is the arrow’s stiffness, which must be matched to your bow’s draw weight and your arrow length. It’s usually the first specification to select.
• Your Draw Length: This determines the finished length you need to cut your arrows to. Your arrow length is the key variable in the GPI calculation.

Simple Formula for Finished Arrow Weight:
(Shaft GPI × Arrow Length in Inches) + Weight of all Components (point, insert, fletchings, nock) = Total Arrow Weight (Grains)

We also offer free of charge Arrow Calculators for you to count your arrow parameters.

I hope this clarifies the meaning of GPI in archery. If you know your bow’s draw weight and your intended use (e.g., target practice or hunting), I can offer more specific guidance on selecting the right arrow spine and weight.