Spear Shaft Calculator

Geometry-based shaft, overhang and assembled spear length calculations.

Geometry-only reference tool. It does not recommend overhang, shaft size, or performance outcomes.

Measurement guidance

Use consistent reference points for every measurement. Measure reference length (G) from the rear shaft position at trigger engagement to your selected muzzle/front reference point.

Manufacturer conventions differ between speargun designs, trigger mechanisms, muzzle geometries and tip systems. Use the same physical points throughout, or use manufacturer-specified dimensions.

Calculator

Select one formula mode at a time.
Configuration is informational. No automatic tip value is assigned.
Units
Rear shaft engagement reference to selected muzzle/front reference.
Body length of the shaft without automatically including tip/adapter contribution.
User-selected or manufacturer-specified overhang. No recommendation is provided.
Enter the installed contribution of the tip and adapter from the manufacturer specification or your own measurement.

Result

Calculated shaft length: —

Reference length (G)
Desired overhang (O)
Units

Optional combined output (when G, S and T are provided)

Shaft-body overhang (S - G)
Total assembled spear length (S + T)
Total assembled overhang ((S + T) - G)

How this works

Mode A:

S = G + O

Mode B:

O = S - G

Mode C:

A = S + T

This calculator performs geometry only. It does not determine optimal overhang, shaft diameter, shaft mass, velocity, penetration, effective range or power.

For measurement conventions and terminology, read How to Measure Spear Shaft Overhang.

For environment-first configuration context, also review the Speargun Size Selector.

Reference tool only. Always follow your equipment manufacturer's specifications; SpearMetric does not guarantee compatibility.