How do you calculate injection pressure from hydraulic pressure?

Multiply the hydraulic system pressure by the machine's intensification ratio, then apply a loss factor for line and check-ring losses. With 2,000 psi hydraulic, a 10:1 ratio, and a 0.92 loss factor you get 18,400 psi of plastic pressure at the screw tip.

What is intensification ratio in injection molding?

It is the ratio of the hydraulic cylinder area to the screw cross-section area, typically 8:1 to 12:1. A 10:1 ratio means every 1 psi of hydraulic pressure becomes roughly 10 psi of plastic pressure on the melt, which is why machine gauges read so much lower than actual cavity pressures.

What is a good injection pressure?

There is no universal number; it depends on resin viscosity and flow length. Most thermoplastics fill at 5,000 to 20,000 psi plastic pressure. The goal is to have at least 20 to 30 percent headroom above the simulated fill requirement so the process isn't running at maximum pressure.

Why is plastic pressure higher than hydraulic pressure?

The screw acts like a hydraulic intensifier: the large hydraulic cylinder pushes a smaller-area screw, multiplying force into pressure by the area ratio. That is why a 2,000 psi hydraulic reading produces 18,400 psi on the melt at a 10:1 ratio with losses.

Hydraulic pressure vs plastic pressure: which one matters?

Plastic pressure is what fills and packs the part, so it is the number that matters for process limits. Hydraulic pressure is just the gauge reading you control; you convert it to plastic pressure with the intensification ratio to know your real capability.

What causes loss between hydraulic and plastic pressure?

Losses come from check-ring leakage, melt flow through the nozzle and runner, and mechanical efficiency. A loss factor of 0.90 to 0.95 is typical; here 0.92 trims the gross 20,000 psi down to 18,400 psi of usable pressure.

Injection Molding calculator

Injection Pressure Calculator

Injection pressure (specific or plastic pressure) is the pressure the melt actually sees at the screw tip, which is many times higher than the hydraulic pressure on the machine gauge because the screw acts as a piston with mechanical advantage. Process engineers and setup technicians use it to confirm a press can deliver enough fill pressure for a given resin and flow length before a mold ever goes in the machine. It matters because short shots, sink, and pack inconsistency are often a pressure-limited problem disguised as a process problem. Knowing the true plastic pressure available lets you compare it against the fill pressure a mold-flow study or resin datasheet demands.

What this calculator does

Estimate required injection pressure from machine hydraulic pressure and intensification ratio for process setup and troubleshooting.
Use this to verify that your press can deliver enough plastic pressure to fill the mold, set initial process parameters, or compare actual vs. available pressure.
It converts machine hydraulic pressure into available plastic pressure at the screw tip using the intensification ratio and a loss factor.

Formula used

Plastic pressure = Hydraulic pressure x Intensification ratio x Loss factor
Compare to estimated fill pressure requirement from flow simulation or resin data

Inputs explained

Hydraulic system pressure during injection:
Intensification ratio (cylinder/screw area ratio):
Pressure loss factor:

How to use the result

Use it when selecting a press for a new tool, transferring a mold between machines, or diagnosing short shots that may be pressure-limited rather than temperature- or speed-related.
It reports the pressure the machine can deliver, not the pressure the part requires; only a mold-flow simulation or measured cavity pressure tells you whether that's enough for your flow length and wall section.

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 injection pressure from hydraulic pressure? Multiply the hydraulic system pressure by the machine's intensification ratio, then apply a loss factor for line and check-ring losses. With 2,000 psi hydraulic, a 10:1 ratio, and a 0.92 loss factor you get 18,400 psi of plastic pressure at the screw tip.
What is intensification ratio in injection molding? It is the ratio of the hydraulic cylinder area to the screw cross-section area, typically 8:1 to 12:1. A 10:1 ratio means every 1 psi of hydraulic pressure becomes roughly 10 psi of plastic pressure on the melt, which is why machine gauges read so much lower than actual cavity pressures.
What is a good injection pressure? There is no universal number; it depends on resin viscosity and flow length. Most thermoplastics fill at 5,000 to 20,000 psi plastic pressure. The goal is to have at least 20 to 30 percent headroom above the simulated fill requirement so the process isn't running at maximum pressure.
Why is plastic pressure higher than hydraulic pressure? The screw acts like a hydraulic intensifier: the large hydraulic cylinder pushes a smaller-area screw, multiplying force into pressure by the area ratio. That is why a 2,000 psi hydraulic reading produces 18,400 psi on the melt at a 10:1 ratio with losses.
Hydraulic pressure vs plastic pressure: which one matters? Plastic pressure is what fills and packs the part, so it is the number that matters for process limits. Hydraulic pressure is just the gauge reading you control; you convert it to plastic pressure with the intensification ratio to know your real capability.

Last reviewed 2026-05-12.