Cooling Time Calculator

Estimate part cooling time from wall thickness, melt temperature, mold temperature, and material thermal properties.

About this calculator

Cooling is the slowest step in most injection molding cycles, often consuming half or more of total cycle time, so wall thickness is the single most important design decision a part designer makes for cycle economics. This calculator uses the classic plate-cooling model from injection molding process engineering: cooling time scales with the SQUARE of wall thickness, because heat has to conduct all the way from the part's mid-plane out to the mold surface, and doubling the thickness roughly quadruples that conduction path's effective time. That squared relationship is why the calculator also reports cooling time at 50% and 150% of your entered thickness — a seemingly modest wall thickness increase can extend cooling time far more than the thickness change itself suggests.

Thermal diffusivity, a material property describing how quickly heat spreads through a substance, sits in the denominator of the cooling equation: higher-diffusivity materials (like unfilled polypropylene) cool faster than lower-diffusivity ones (like glass-filled nylons) at the same wall thickness. Melt, mold, and ejection temperatures set the logarithmic temperature-ratio term in the formula — a larger gap between melt and ejection temperature (relative to mold temperature) extends cooling time, since more heat has to leave the part before it is rigid enough to eject safely.

Inputs

Wall Thickness

Melt Temperature

°F

Mold Temperature

°F

Ejection Temperature

°F

Thermal Diffusivity

×10⁻⁷ m²/s

Tab to move between fields

Results

Cooling Time

10.05 sec

Cooling at 50% Thickness2.51 sec

Cooling at 150% Thickness22.61 sec

Melt-to-Mold ΔT180 °C

Cooling as % of Cycle55.7%

How to Use This Calculator

Enter wall thickness (mm) — the thickest cross-section of the part controls cooling time.
Set melt temperature (°C) and mold temperature (°C) for your material and process.
Enter ejection temperature (°C) — the temperature at which the part is stiff enough to eject.
Review calculated cooling time (sec), and how it varies with wall thickness.
Cooling typically represents 50–70% of total cycle time — minimize it by reducing wall thickness.

How the result changes with Wall Thickness

Wall Thickness	Cooling Time
1.25	2.51 sec
1.88	5.68 sec
3.75	22.61 sec
6.25	62.81 sec

What each input means

Wall Thickness: Maximum wall thickness of the part in mm.
Melt Temperature: Material melt/injection temperature (e.g., PP: 220, ABS: 230, PC: 300).
Mold Temperature: Mold surface temperature during cooling.
Ejection Temperature: Temperature at which the part is rigid enough to eject.
Thermal Diffusivity: Material thermal diffusivity (PP: 0.9, ABS: 1.1, PA66: 1.5, PC: 1.4).

How this is calculated

Worked example, using the default values

Identify Input Parameters
5 parameters
Wall Thickness = 2.5, Melt Temperature = 230, Mold Temperature = 50, Ejection Temperature = 90, Thermal Diffusivity = 1.1 = 5 input(s) provided
Calculate Cooling Time
Cooling Time = max(round(coolingTimeSeconds * 100) / 100
10.05 = 10.05
Calculate Cooling at 50% Thickness
Cooling at 50% Thickness = max(thinWallTime
2.51 = 2.51
Calculate Cooling at 150% Thickness
Cooling at 150% Thickness = max(thickWallTime
22.61 = 22.61

Engine last updated August 26, 2026. Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does cooling time depend on the SQUARE of wall thickness?

Heat has to conduct from the part's thickest interior point out to the mold surface, and the physics of transient heat conduction through a plate scales with the square of that conduction distance, not linearly with it. That's why doubling wall thickness roughly quadruples cooling time rather than doubling it — a small thickness increase can meaningfully hurt cycle time.

What is thermal diffusivity and why does it matter here?

Thermal diffusivity measures how quickly a material conducts heat relative to how much heat it stores, combining thermal conductivity, density, and specific heat into one property. Materials with higher diffusivity, like unfilled polypropylene, shed heat and cool faster at a given wall thickness than lower-diffusivity materials like glass-filled nylons, all else being equal.

How can I reduce cooling time without changing the material?

Since cooling time scales with the square of wall thickness, reducing wall thickness anywhere it's structurally safe to do so has an outsized payoff compared to other levers. Increasing the temperature gap the part needs to cool through, by lowering mold temperature within the material's process window, also helps, though it can affect surface finish and internal stress.

Does cooling time include the whole injection molding cycle?

No, this figure covers only the cooling phase — the time the part spends solidifying in the closed mold before ejection. Total cycle time also includes fill time, pack/hold time, and mold open/close and ejection time, so cooling typically represents a large share of the cycle but not the entire cycle itself.

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