How do you calculate mold cooling water flow?

Divide the heat load by the product of water's specific heat and the allowable temperature rise, then multiply by a safety factor. With 12 kW, a 3°C rise, and a 1.2 factor, the base flow of 36 becomes about 43.2 L/min.

What temperature rise should I allow across a mold?

Keep the water in-to-out rise small, typically 2 to 3°C, so the mold stays thermally uniform. A larger allowed rise lowers the required flow but creates temperature gradients across the cavity that hurt part quality.

Why include a safety factor for cooling water flow?

Real systems lose capacity to scale, biofilm, hose kinks, and restrictive fittings over time. A 1.2 factor here adds 20 percent headroom, taking the 36 L/min base requirement up to 43.2 L/min.

What flow rate gives turbulent cooling?

Turbulent flow (Reynolds above roughly 4,000) is the goal because it transfers heat far better than laminar flow. The total flow from this calculator must be split so each channel individually stays turbulent.

How much heat does a mold need to remove?

The heat load equals the energy the molten plastic gives up as it cools per unit time, roughly shot mass times resin enthalpy drop divided by cycle time, plus any hot-runner load. Estimate it from throughput and resin properties.

Does higher flow always mean better cooling?

Up to a point. Once flow is solidly turbulent, extra flow yields diminishing returns and just raises pump load and pressure drop. Size for turbulent flow plus the safety margin, not for the highest possible number.

Injection Molding calculator

Cooling Water Flow Calculator

Cooling water flow is what actually carries heat out of an injection mold, and undersizing it is a silent killer of cycle time and part consistency. This calculator sizes the required flow in litres per minute from the heat you need to remove, the temperature rise you allow across the mold, and a safety factor for fouling, scale, and line restrictions. Mold and process engineers use it to specify chiller and pump capacity, verify that a manifold can deliver enough flow per circuit, and confirm the system can sustain turbulent flow — the regime where heat transfer is many times better than laminar. Get this number wrong and the mold runs hot, dimensions drift, and the press never reaches its rated cycle.

What this calculator does

Calculate required cooling water flow rate from heat load, allowable temperature rise, and a safety margin for scaling or restrictions.
Use this when specifying mold cooling circuits, sizing chillers, or troubleshooting uneven cooling or hot spots in the mold.
It computes the cooling water flow rate in L/min needed to carry a given heat load away at a chosen temperature rise, including a safety margin.

Formula used

Base flow = Heat load / (Water specific heat x Temperature rise)
Required flow = Base flow x Safety factor (result in L/min)

Inputs explained

Heat load to remove from mold:
Allowable water temperature rise:
Safety factor for fouling/restrictions:

How to use the result

Use it when specifying a chiller or pump, sizing cooling circuits, or checking whether an existing system can keep a mold at temperature.
It sizes total flow but does not guarantee turbulent flow in each individual channel; flow must still be distributed so every circuit reaches a Reynolds number above about 4,000.

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 mold cooling water flow? Divide the heat load by the product of water's specific heat and the allowable temperature rise, then multiply by a safety factor. With 12 kW, a 3°C rise, and a 1.2 factor, the base flow of 36 becomes about 43.2 L/min.
What temperature rise should I allow across a mold? Keep the water in-to-out rise small, typically 2 to 3°C, so the mold stays thermally uniform. A larger allowed rise lowers the required flow but creates temperature gradients across the cavity that hurt part quality.
Why include a safety factor for cooling water flow? Real systems lose capacity to scale, biofilm, hose kinks, and restrictive fittings over time. A 1.2 factor here adds 20 percent headroom, taking the 36 L/min base requirement up to 43.2 L/min.
What flow rate gives turbulent cooling? Turbulent flow (Reynolds above roughly 4,000) is the goal because it transfers heat far better than laminar flow. The total flow from this calculator must be split so each channel individually stays turbulent.
How much heat does a mold need to remove? The heat load equals the energy the molten plastic gives up as it cools per unit time, roughly shot mass times resin enthalpy drop divided by cycle time, plus any hot-runner load. Estimate it from throughput and resin properties.

Last reviewed 2026-05-12.