How do you calculate cushion percentage?

Divide the cushion amount by the total shot size and multiply by 100. A 3.5 g cushion on a 52 g shot is (3.5 / 52) x 100 = 6.73%, which sits in the typical 5%-10% target band.

What is a good cushion percentage in injection molding?

Most processes target 5% to 10% of shot size. The 6.73% in the example is a solid, centered value. Below about 3% you risk the screw bottoming out; above 10% you carry excess melt and waste residence time.

Why is cushion important?

The cushion is the melt pad that lets the screw keep transmitting hold pressure after fill. Without it the screw hits a hard stop, hold pressure collapses, and parts show sink marks, voids, or short shots.

What causes cushion to drift over a run?

A worn or leaking check ring (non-return valve) is the most common cause; melt slips back over the ring and the cushion shrinks shot to shot. Material viscosity changes and transfer-position drift also move it.

Cushion vs shot size - what is the difference?

Shot size is the total material injected per cycle; cushion is the small leftover pad after pack and hold. Cushion percentage relates the two so you can judge whether the pad is proportionate to the shot.

Can cushion be too high?

Yes. A cushion well above 10% means you are recovering more material than needed, increasing residence time and degradation risk, and it can signal an oversized barrel or a transfer position set too early.

Injection Molding calculator

Cushion Percentage Calculator

Cushion is the small pad of melt left in front of the screw at the end of the hold phase, and cushion percentage expresses it as a share of total shot size. Process technicians watch this number because the cushion is what transmits pack and hold pressure into the cavity; too little and the screw bottoms out, losing pressure and causing sink or short shots, too much and you are wasting residence time and risking degradation. Most stable processes run a cushion of roughly 5% to 10% of shot size. Tracking cushion percentage shot-to-shot is one of the fastest ways to catch a check-ring leak or a drifting process.

What this calculator does

Calculate the screw cushion as a percentage of total shot size to verify consistent pack pressure transfer.
Use this to check that the cushion (material left in front of the screw after injection) is within the recommended 5% to 10% of shot size for consistent part quality.
It computes the cushion as a percentage of total shot size by dividing cushion amount by shot size and multiplying by 100.

Formula used

Cushion percentage = (Cushion amount / Total shot size) x 100
Target range is typically 5% to 10% of shot size

Inputs explained

Cushion amount: Weight or volume of resin remaining in front of the screw after injection complete. Read from machine controller.
Total shot size: Full shot weight (parts + runner + cushion). This is the total material metered per cycle.

How to use the result

Use it when validating a new process or monitoring a running job to confirm the cushion stays inside the 5%-10% target band.
The percentage is only as good as your cushion reading; a worn check ring can give a stable-looking number while leaking, so trend it alongside actual fill and pack pressure.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 9,635 plastics product manufacturing establishments employing about 677,302 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate cushion percentage? Divide the cushion amount by the total shot size and multiply by 100. A 3.5 g cushion on a 52 g shot is (3.5 / 52) x 100 = 6.73%, which sits in the typical 5%-10% target band.
What is a good cushion percentage in injection molding? Most processes target 5% to 10% of shot size. The 6.73% in the example is a solid, centered value. Below about 3% you risk the screw bottoming out; above 10% you carry excess melt and waste residence time.
Why is cushion important? The cushion is the melt pad that lets the screw keep transmitting hold pressure after fill. Without it the screw hits a hard stop, hold pressure collapses, and parts show sink marks, voids, or short shots.
What causes cushion to drift over a run? A worn or leaking check ring (non-return valve) is the most common cause; melt slips back over the ring and the cushion shrinks shot to shot. Material viscosity changes and transfer-position drift also move it.
Cushion vs shot size - what is the difference? Shot size is the total material injected per cycle; cushion is the small leftover pad after pack and hold. Cushion percentage relates the two so you can judge whether the pad is proportionate to the shot.

Last reviewed 2026-05-12.