Arrow spine is the measure of how stiff a shaft is. Match it correctly to your bow setup and your arrows fly straight, group tightly, and recover quickly from the paradox at release. Get it wrong and you'll see inconsistent flight, poor groups, and erratic performance with broadheads — no matter how well you shoot.
The chart below is based on the AMO/ATA standard for 100 grain field points. Find your draw weight in the left column, then move across to your arrow length to get your recommended spine.
| Draw weight | 25–26" | 27–28" | 29–30" | 31" |
|---|---|---|---|---|
| 40–45 lb | 500 | 600 | 600 | 600 |
| 46–52 lb | 400 | 500 | 500 | 600 |
| 53–58 lb | 400 | 400 | 500 | 500 |
| 59–65 lb | 340 | 400 | 400 | 400 |
| 66–72 lb | 300 | 340 | 400 | 400 |
| 73–80 lb | 250 | 300 | 340 | 340 |
Using broadheads heavier than 100 gr? Go one step stiffer. 125 gr broadheads add front-of-centre weight that makes your arrow act weaker. At 65 lb / 28" with 125 gr broadheads, choose 340 instead of 400.
Arrow length is measured from the bottom of the nock groove to the end of the shaft — not including the point. Use the length you'll actually shoot, after any cutting, not the raw shaft length you ordered.
Draw weight means your peak draw weight at your actual draw length — not the bow's maximum. If your bow is set to 65 lb, use 65 lb regardless of what it can be cranked to.
When you fall between two spine options, choose the stiffer one (lower number). An arrow that's slightly too stiff forgives more than one that's too weak. Underspined arrows are the main cause of broadhead flight problems.
Go one step stiffer. Extra front weight increases dynamic flex and makes the shaft act weaker.
You can go one step weaker. Less front weight reduces flex at release.
Cutting an arrow shorter effectively stiffens it. Cut 1" shorter = roughly one step stiffer.
Hunters should err stiffer for broadhead forgiveness. Target and 3D shooters can shoot the chart's recommendation straight.
Too weak (number too high) — The arrow flexes too much on release and doesn't recover properly. You'll see left/right tears in paper, inconsistent groups, and broadheads that fly differently to field points. This is the most common problem.
Too stiff (number too low) — The arrow doesn't flex enough and kicks the other direction. Less common than underspined, and generally forgiving at field-point distances, but still causes broadhead issues at longer range.
After selecting a spine, shoot through paper from 6–8 feet. A round bullet hole means the arrow is flying cleanly. Any tear tells you the direction and type of correction needed. See paper tuning vs walk-back tuning for the full process.
Hunting: Use the chart recommendation or one step stiffer. Broadheads punish underspined arrows more than field points. Most hunting arrows run 340–500 spine for typical draw weights of 55–70 lb.
3D archery: Shoot the chart recommendation. 3D focuses on consistent flight and flat trajectory, which the recommended spine is optimised for. Slightly lighter arrows (higher GPP efficiency) help at the longer 3D distances.
Indoor / target (20 yards): At short distances, spine tolerance is wider. You can go one step weaker without visible impact on groups. Many indoor shooters use lighter, faster arrows for flatter trajectory at 20 metres.
Once you know your spine and arrow weight, use the sight tape generator to calculate your exact sight marks. Enter your arrow weight and the generator shows your grains-per-pound ratio alongside the tape.