Net part weight only
- Ignores sprue, runner, and gate mass
- Understates resin usage on cold runner tools
- Makes cavitation math look cheaper than reality
Glossary
What Is Shot Size? Injection Molding Explained
Shot size covers everything the screw pushes forward in one cycle, not just your part.
Glossary
Shot size is how much plastic the screw delivers in one stroke
Short shots and flash both send buyers hunting the wrong root cause.
Shot size describes the mass or volume of material the injection unit plasticates and pushes forward in a single cycle. It must cover parts, runners, gates, and the cushion the process needs.
A short shot is not always a tooling defect. Transfer position, shot size setting, and venting all belong in the same troubleshooting thread.
On multi cavity tools, imbalance shows up as one cavity short while others fill. That pattern points to runner balance or gate detail, not only machine shot capacity.
Glossary
How shot size shows up on real programs
Library photos illustrate molding and tooling context for this term.
- Use the term in RFQs with geometry and material context, not in isolation.
- Link to the design guide when the term affects steel or part design.
- Upload CAD when the term changes tooling scope or piece price.
Mass balance
Net part weight versus full shot
Buyers comparing supplier quotes should know what each weight line includes.
Full shot accounting
- Includes feed path scrap on cold runners
- Separates regrind policy from virgin resin purchase
- Aligns with how production planning buys resin
Troubleshooting
Before you blame the tool for a short fill
Share this list with your molder when photos show incomplete fill.
Which cavity or region is short, with a photo if possible
Material lot and drying record for hygroscopic grades
Recent change to shot size, transfer, or back pressure
Gate freeze off time relative to pack completion
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Sprue
First channel from the nozzle into the runner.
SprueRunner
How plastic reaches each gate on multi cavity layouts.
RunnerSink marks article
When thick sections steal pack from thin regions.
Sink marks articleVisual reference
Photos from molding and tooling programs
Images are selected from the NetProto Forge media library for this topic.
Injection molded production parts on a tray
Injection molded production parts on a tray
Engineer reviewing a molded part drawing
Engineer reviewing a molded part drawing
Plastic housing components from a steel tool
Plastic housing components from a steel tool
FAQ
Shot size questions
Does shot size equal part weight?
No. Part weight is only the molded component. Shot size includes the feed path and cushion.
Can shot size limit cavitation?
Yes. The injection unit must physically deliver the total molded volume each cycle.
Where do I learn runner and gate sizing rules?
Start with the design guide hub for gate location and runner design spokes.
Next step
Connect shot issues to DFM
Upload CAD when fill balance or short shots trace back to geometry, not just machine settings.