Archery term
Grains per Inch (GPI)
What does Grains per Inch (GPI) mean?
Grains per inch (GPI) is the mass of an arrow shaft per inch of its length, usually listed by the shaft manufacturer. It describes the bare shaft, not the finished arrow; point, insert, nock, and fletching add more mass. Use cut shaft length to estimate shaft mass, then add every component.
Primary source for this term: Easton 2021 Target Product Guide (2021)
Why it matters
Multiply the shaft’s GPI by its cut length for an estimate of shaft mass, then add the components. For example, a 7-GPI shaft cut to 29 inches weighs about 203 grains before components. Confirm the actual model specification because shaft designs and listed tolerances vary.
What to check
- Multiply the maker’s GPI by the cut shaft length to estimate bare-shaft mass.
- Add point, insert, nock, and fletching mass for the finished arrow.
- GPI describes mass, not spine or minimum finished-arrow weight.