Shot Size Calculator
Calculate the required shot size, barrel capacity, and recommended screw diameter. The calculator accounts for the number of cavities, runner weight, and material cushion — key parameters for injection machine selection.
Input Parameters
Results
Fill in the data and click Calculate
ARGUS automatically selects the machine based on shot size, clamping force, and mold parameters
Shot size is one of the machine selection parameters — ARGUS simultaneously accounts for clamping force, tie-bar spacing, mold height, and required injection speed.
How do we calculate shot size?
Shot size is the total mass of material injected into the mold in one cycle. It comprises the weight of all parts (part weight × number of cavities), the runner weight, and the material cushion. Correct shot size selection is critical for choosing the right injection machine — the barrel should be utilized in the range of 20–80% of its capacity.
The calculator applies the standard shot size selection formula accounting for the material cushion and converting to barrel capacity.
mrequired = mshot × (1 + cushion/100)
Vshot = mrequired / ρ
mpart — part weight [g]
n — number of cavities
mrunner — runner weight [g]
cushion — material cushion [%]
ρ — material density [g/cm³]
The material cushion is the reserve of material remaining in front of the screw after the injection phase. A typical value is 5–15% of shot size. The cushion ensures that packing pressure can be maintained and compensates for volumetric shrinkage during solidification. Too small a cushion (<5%) risks short shots; too large (>20%) extends material residence time in the barrel.
Barrel and screw selection
Barrel capacity should be selected so that the shot size represents 20–80% of its volume. Utilization below 20% risks thermal degradation of the material (excessive residence time), while above 80% leaves insufficient cushion.
Acceptable — 20–80% of capacity
Risky — <20% (degradation) or >80% (no cushion)
Screw diameter is linked to barrel capacity and determines the available injection pressure and plasticizing rate. Typical diameters are 25–90 mm. Smaller diameters (25–40 mm) are used for small parts and precision machines; larger diameters (60–90 mm) for large parts and multi-cavity molds.
Hot runner system
In a hot runner system the runner weight is 0 g, which significantly reduces the required shot size and improves material utilization. When analyzing the cost-effectiveness of a hot runner system, compare the material cost lost to the cold runner against the investment cost of the hot runner system.
ARGUS automatically selects the machine based on shot size and clamping force
See it for yourself — book a presentation and discover how ARGUS connects process calculations with your plant's machine database.