Shot Size Calculator

Calculate injection molding shot weight including cavities, runner, and cushion. This practical tool is an engineering estimate—validate decisions against machine, material, mold, and process data.

Formula and method

Shot mass includes all cavity parts, runner/sprue, and the selected cushion.

Inputs and units

Enter measured or specified values in the displayed units. Keep units consistent; results are rounded for practical planning. This first release uses the displayed engineering units rather than a unit-switcher.

Worked example

(45 g × 4 cavities + 12 g runner) × 1.10 cushion allowance = 211.2 g.

Use this before selecting an injection unit

Build the complete shot from every cavity, runner or sprue, and the process cushion. Compare the result with the machine documentation for the actual resin and screw.

What changes the result most

Cavity count, cold-runner mass, and cushion policy. Hot-runner systems change runner waste but still require a documented shot.

Common mistake

Treating part weight alone as the shot ignores runners and can leave no stable cushion.

Interpretation, assumptions, and limitations

This tool provides an estimate for planning and education. It does not replace machine maker limits, material data sheets, mold trials, cavity-pressure data, process validation, or qualified engineering review.

FAQ

Can I use this as a final production setting?

No. Confirm with validated process data and the applicable machine and material documentation.

Why can the real result differ?

Geometry, melt behavior, pressure loss, material lot, temperature, cooling layout, and operating practice can materially affect results.