How do you calculate injection molding cooling time?

Multiply a resin cooling factor (in sec/mm²) by the wall thickness raised to a geometry exponent, usually 2. With a 2.5 mm wall, a 3.2 factor, and an exponent of 2, cooling time is 3.2 x 2.5² = 16 seconds.

Why does cooling time scale with the square of wall thickness?

Heat conducts out of the part by diffusion, and diffusion distance grows with the square root of time — so doubling wall thickness roughly quadruples cooling time. A 2.5 mm wall cooling in 16 seconds would jump to about 64 seconds at 5 mm.

What is a typical cooling factor for plastics?

It depends on resin thermal diffusivity, melt and mold temperatures; values commonly fall in the 2 to 4 sec/mm² range for general thermoplastics. The 3.2 used here is representative of a mid-range commodity resin.

Is cooling time the same as cycle time?

No. Cooling time is only the cooling phase. Total cycle also includes injection, pack and hold, mold open, ejection, and close — typically adding several seconds on top of the 16-second cooling estimate.

How can I reduce cooling time?

Reduce the thickest wall section, lower mold temperature within spec, improve cooling-line layout or add conformal cooling, and core out heavy sections. Because of the squared relationship, shaving wall thickness gives the biggest gain.

What geometry exponent should I use?

Use 2 for the standard plate-cooling assumption, which is the most common. Some references use slightly different exponents for specific geometries, but 2 is the safe default for flat walls.

Injection Molding calculator

Mold Cooling Time Calculator

Cooling time is the single largest chunk of most injection molding cycles, often 60 to 80 percent of total cycle, and it scales with the square of wall thickness — so thick sections punish you disproportionately. This calculator estimates the cooling phase using the classic relationship between wall thickness, a resin-specific cooling factor derived from thermal diffusivity, and a geometry exponent (typically 2). Tooling engineers and molders use it to set realistic cycle expectations, justify wall-thickness reductions in design reviews, and predict the payback of conformal cooling. Getting the cooling estimate right early prevents the painful discovery that a part will never hit its target cycle no matter how the press is tuned.

What this calculator does

Estimate cooling time from melt temperature, mold temperature, part wall thickness, and material thermal properties.
Use this to estimate cooling time during mold design, optimize cycle time, or validate simulation results against a simplified analytical estimate.
It computes the cooling phase duration in seconds by multiplying the resin cooling factor by wall thickness raised to the geometry exponent.

Formula used

Cooling time = Cooling rate factor x (Wall thickness ^ Geometry exponent)
This is the cooling phase only; add injection, pack, open, and eject for full cycle

Inputs explained

Maximum part wall thickness:
Cooling rate factor (thermal diffusivity based):
Thickness geometry exponent:

How to use the result

Use it during part and tool design, cycle-time quoting, or when evaluating whether thinner walls or better cooling will pay off.
It models cooling as one-dimensional through the thickest wall and ignores poor cooling-line layout, hot spots, and crystallization effects, so real cycles often run longer.

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 molding cooling time? Multiply a resin cooling factor (in sec/mm²) by the wall thickness raised to a geometry exponent, usually 2. With a 2.5 mm wall, a 3.2 factor, and an exponent of 2, cooling time is 3.2 x 2.5² = 16 seconds.
Why does cooling time scale with the square of wall thickness? Heat conducts out of the part by diffusion, and diffusion distance grows with the square root of time — so doubling wall thickness roughly quadruples cooling time. A 2.5 mm wall cooling in 16 seconds would jump to about 64 seconds at 5 mm.
What is a typical cooling factor for plastics? It depends on resin thermal diffusivity, melt and mold temperatures; values commonly fall in the 2 to 4 sec/mm² range for general thermoplastics. The 3.2 used here is representative of a mid-range commodity resin.
Is cooling time the same as cycle time? No. Cooling time is only the cooling phase. Total cycle also includes injection, pack and hold, mold open, ejection, and close — typically adding several seconds on top of the 16-second cooling estimate.
How can I reduce cooling time? Reduce the thickest wall section, lower mold temperature within spec, improve cooling-line layout or add conformal cooling, and core out heavy sections. Because of the squared relationship, shaving wall thickness gives the biggest gain.

Last reviewed 2026-05-12.