How much should your arrow weigh? That’s a loaded question. An arrow’s weight helps determines how it flies. An arrow’s path from bow to target seems simple, but arrow weight partly determines the physics of each shot.
Arrows are propelled by kinetic energy produced by drawing a bow. That energy transfers to the arrow when the archer releases the bowstring. An arrow’s weight helps determine its speed, drop rate and target penetration. Beginners, bowhunters and competitive archers all try to maximize arrow performance by trying different weights.
Arrows come in three weight categories: light, midweight and heavy. Lighter arrows fly faster and can group more tightly, but they’re often harder to tune. Heavier arrows fly slower but resist wind better and penetrate deeper.
Shooting the wrong arrow weight for a bow can damage equipment and harm the archer. That’s why manufacturers design bows for specific minimum arrow weights.
How do you calculate your arrow’s weight to ensure you’re shooting the right setup for your bow? It isn’t as simple as setting the arrow on a scale. Let’s review how to calculate arrow weights.
Grains Per Inch
Grains per inch is the industry standard for measuring arrow weights. An arrow’s GPI determines the arrow shaft’s weight. It includes the arrow’s length, diameter, wall thickness and shaft material. The GPI number does not include the nock, insert, point or fletchings. Manufacturers provide details about the arrow’s GPI on their website and product packaging.
Using GPI calculations, a light shaft weighs 5 to 6 grains per inch, a midweight shaft weighs 7 to 9 grains per inch, and a heavy shaft weighs 10 or more grains per inch.
Grains Per Pound
GPI is often confused with GPP – grains per pound – but these calculations differ greatly. GPP is the arrow’s total weight divided by the bow’s poundage for shooting that arrow. The GPP total includes the weight of the shaft, nock, insert, point and fletchings.
A light arrow has a finished GPP of 5 to 6.5 grains for each pound of draw weight. A midweight arrow weighs between 6.5 and 8 grains. Heavy arrows weigh over 8 grains.
Front of Center
To further complicate arrow-weight calculations, you must know how weight is distributed across the arrow. The arrow’s point is heavier than its fletchings. A front-of-center number describes the percentage of an arrow’s total weight in its front half. FOC determines an arrow’s accuracy and is critical for long-range shots.
Easton Archery’s website helps determine your arrow’s FOC:
- Divide the arrow’s length (distance from the bottom of the nock groove to the shaft’s end) by 2.
- Find the balance point. This is where the arrow balances perfectly. Mark the point, and measure from there to the nock’s throat.
- Subtract the center of the arrow measurement (calculated in Step 1) from the balance point (calculated in Step 2).
- Multiply Step 3’s answer by 100.
- Divide the answer from Step 4 by the arrow’s overall length. This number is the arrow’s FOC measurement.
Properly balanced arrows have an FOC of 7 to 15 percent.
Light vs. Heavy Arrows
Now that you know how to calculate an arrow’s weight, it’s important to determine what weight class or arrow best suits your bow and shooting needs. Deciding whether to shoot lightweight or heavy arrows depends on several factors.
Lighter arrows fly faster than heavier arrows. That increased speed helps arrows fly straighter, which can create tighter groups. Lighter arrows are also more forgiving on longer shots because they drop more slowly than do heavier arrows. Lighter arrows, however, can be more difficult to tune and less forgiving on windy days. Follow your bow’s guidelines for arrow weight because arrows that are too light won’t absorb enough energy from the bowstring, which causes bow vibrations that can damage equipment.
Heavier arrows are slower but absorb more of the bow’s kinetic energy. Bowhunters often choose heavier arrows for deeper penetration and better wind-bucking traits. Because heavier arrows absorb more energy, they’re also quieter to shoot.
If you have questions about arrow weights or want to explore which arrows are right for your bow, visit a nearby archery shop.