K2 Arrow Co. / Technical Tools

Arrow spine & performance calculator

Build Your Arrow

Build a K2 or other arrow around your real bow specifications. The tool will not recommend a spine more than .0125 inch weak, while every listed spine remains selectable for comparison.

Enter your setup
Arrow shaft
GPI updates automatically for K2 shafts and becomes editable when Other is selected.
Bow setup
Rear arrow build

Cut length is measured from the throat of the nock to the cut end of the carbon shaft. Enter the actual total weight for one wrap and the weight of one vane or feather.

Recommendation safety rule No recommended shaft may calculate more than .0125 inch weak. Weaker choices remain selectable for comparison.

Recommended static spine

300 spine

Arrow weight 441 gr Shaft and all entered components. Adhesive is not included.
Estimated speed 280 fps IBO-based estimate with a 10 fps real-world deduction.
Estimated finished FOC 17.4% Calculated from estimated component mass locations.
Estimated KE 76.6 ft-lb Calculated at the estimated launch speed.
Estimated momentum 0.548 slug-ft/s Momentum shown in slug-feet per second.
Finished grains per pound 6.30 GPP Finished arrow weight divided by measured draw weight.
Selected static spine .300 in Nominal static deflection under the standard spine test.
Dynamic spine estimate .299 eq. Equivalent static-spine demand interpolated within the manufacturer chart cell.
Setup match Optimal

.001 in weaker than the estimated dynamic demand

The recommendation begins with Easton's published compound-bow shaft-selection matrix and uses the entered cut shaft length. The chart values are interpolated between whole-inch length columns for the displayed estimate. Point weight and insert/outsert weight are converted to equivalent bow-weight corrections using Easton's published rules before the chart is evaluated. Increasing either front weight makes the dynamic reaction weaker and moves the equivalent demand toward a stiffer static shaft. The displayed dynamic-demand value updates to the nearest .001 inch.

Nock, wrap, and fletching mass stays in the rear-build equation. Increasing that rear mass stiffens the arrow's dynamic reaction, so the equivalent static-deflection demand moves higher.

A conservative .008-inch weak-reaction allowance is built into the dynamic calculation so borderline setups move toward the stiffer shaft.

The calculator chooses from the available spines for the selected K2 shaft. Other mode evaluates the spine and GPI entered by the user. A recommended shaft is never allowed to exceed the dynamic-demand estimate by more than .0125 inch, but weaker choices remain available for comparison.

Static spine is a standardized shaft-deflection measurement. Dynamic spine describes how the complete arrow reacts when launched and is affected by variables that cannot all be measured through a website form. The displayed dynamic number is therefore an equivalent-demand estimate, not a laboratory measurement of the arrow in flight.

Speed uses the 70-pound, 30-inch, 350-grain IBO reference with corrections for measured draw weight, draw length, and finished arrow weight, followed by a 10 fps real-world deduction. FOC is estimated from component locations and should be confirmed by physically balancing a finished arrow.

Use this result as a starting point. Confirm the finished hunting arrow with paper tuning, bare-shaft tuning, and broadhead verification before hunting.

Research basis: Easton Hunting Shaft Selection Chart and Victory Archery Arrow Guide.

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Calculator results are equipment-selection estimates, not a guarantee of tune or safe arrow compatibility. Always follow the bow and arrow manufacturers’ minimum arrow-weight and safety requirements.