How do I calculate injection molding cycle time?

Cycle time is injection plus pack and hold plus cooling plus mold open, ejection, and close. Cooling usually dominates, often 60 to 70 percent of the total, and scales with the square of wall thickness. The Injection Molding Cycle Time calculator sums these phases, and Mold Cooling Time estimates the cooling portion from wall thickness and melt and mold temperatures. Shaving two seconds of cooling on a 24-second cycle raises Mold Parts Per Hour by roughly 8 percent.

How much clamp tonnage do I need for a part?

Clamp tonnage is projected area times cavity pressure, then a safety factor. A common rule is 2 to 5 tons per square inch of projected area depending on resin and flow length. The Clamp Tonnage calculator multiplies total projected area, including runners, by your cavity pressure so a 30 square inch shot at 3 tons per square inch needs about 90 tons. Undersizing flashes the parting line; oversizing wastes Injection Machine Hour Rate on a bigger press.

What is a healthy cushion percentage and why does it matter?

Cushion is the material left in front of the screw at the end of hold, and it should stay small but never zero, commonly around 3 to 10 percent of shot size or about 3 to 6 mm on a mid-size barrel. The Cushion Percentage calculator checks yours against shot size. Too little cushion means the screw bottoms out and pack pressure drops, causing sinks and short shots; too much wastes Barrel Residence Time and risks resin degradation.

How do I calculate resin cost per part including the runner?

Add part weight and runner weight, divide the runner across the number of cavities, then multiply by resin price per pound. The Resin Cost Per Part calculator combines Plastic Part Weight and Runner Weight with material cost, so a 40-gram part with 8 grams of runner per cavity at 1.20 dollars per pound runs about 0.127 dollars. A cold runner adds real cost, which is why Regrind Percentage and Plastic Regrind Savings matter on high-runner parts.

How long do I need to dry a hygroscopic resin?

Drying time depends on the resin and target moisture: nylon and PET often need 4 to 6 hours at 175 to 180 F, while ABS may need 2 to 4 hours at 80 C. The Resin Drying Time calculator sets time from resin and throughput, and Resin Dryer Capacity confirms the dryer and Hopper Residence Time keep pace with the press. Molding wet nylon or PET causes splay, brittleness, and hydrolytic degradation that no process tweak fixes.

How do I set the machine hour rate for a molded-part quote?

The Injection Machine Hour Rate calculator rolls depreciation, floor space, energy, maintenance, and operator time into a dollars-per-hour figure by press tonnage. Multiply that rate by cycle time and divide by cavity count to get machine cost per part. Combine it with Resin Cost Per Part and Mold Amortization Cost to build a full quote, and use Mold Changeover Cost to decide economic run lengths, since short runs spread setup across fewer parts.

Manufacturing calculator category

Injection Molding & Plastics Processing calculators

This category covers the process and cost math behind injection molding: cycle time, clamp tonnage, shot size, cavitation, resin usage, drying, and cooling. It is built for process engineers, molding estimators, and plant planners who need concrete numbers to run a mold, size a press, and cost a molded part.

What this hub covers

Calculators for injection molders and plastics processors: cycle time, clamp tonnage, shot size, cavitation, resin cost per part, regrind, drying, and cooling.
Browse injection molding & plastics processing calculators for manufacturing planning, quoting, quality, capacity, and operations decisions.

Best calculators in this category

Injection Molding Cycle Time: Estimate total injection molding cycle time from shot count, press cycling rate, and non-productive time allowance.
Clamp Tonnage: Calculate required clamp force from projected part area, average cavity pressure, and a safety factor for flash prevention.
Shot Size: Calculate total shot size from part weight, runner weight, number of cavities, and an overfill safety factor.
Cushion Percentage: Calculate the screw cushion as a percentage of total shot size to verify consistent pack pressure transfer.
Plastic Part Weight: Estimate part weight from CAD volume and resin density for shot sizing and cost estimating before mold trials.
Runner Weight: Estimate cold runner system weight from runner volume, resin density, and a geometry factor for sprue and sub-runners.
Mold Cavitation: Determine the optimal number of mold cavities from annual demand, available press cycle time, and production hours.
Mold Parts Per Hour: Calculate parts per hour output from cycle time and mold cavitation to plan production capacity and press scheduling.
Resin Cost Per Part: Calculate material cost per molded part from part weight, runner scrap allocation, and resin price per kilogram.
Regrind Percentage: Calculate the regrind content as a percentage of total shot weight to stay within resin supplier and quality limits.
Plastic Regrind Savings: Estimate annual material cost savings from using regrind instead of 100% virgin resin in injection molding production.
Scrap Resin Cost: Calculate the annual cost of scrapped resin from rejects, purging, startup waste, and non-recoverable material.

Common manufacturing problems solved

injection molding
plastic processing
clamp tonnage
shot size
resin cost
mold cavitation

Live market signals for this industry

The producer price index for plastic resins and materials stands at 310.753 (BLS, Jun 2026), up 17.2% 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).

Category questions

How do I calculate injection molding cycle time? Cycle time is injection plus pack and hold plus cooling plus mold open, ejection, and close. Cooling usually dominates, often 60 to 70 percent of the total, and scales with the square of wall thickness. The Injection Molding Cycle Time calculator sums these phases, and Mold Cooling Time estimates the cooling portion from wall thickness and melt and mold temperatures. Shaving two seconds of cooling on a 24-second cycle raises Mold Parts Per Hour by roughly 8 percent.
How much clamp tonnage do I need for a part? Clamp tonnage is projected area times cavity pressure, then a safety factor. A common rule is 2 to 5 tons per square inch of projected area depending on resin and flow length. The Clamp Tonnage calculator multiplies total projected area, including runners, by your cavity pressure so a 30 square inch shot at 3 tons per square inch needs about 90 tons. Undersizing flashes the parting line; oversizing wastes Injection Machine Hour Rate on a bigger press.
What is a healthy cushion percentage and why does it matter? Cushion is the material left in front of the screw at the end of hold, and it should stay small but never zero, commonly around 3 to 10 percent of shot size or about 3 to 6 mm on a mid-size barrel. The Cushion Percentage calculator checks yours against shot size. Too little cushion means the screw bottoms out and pack pressure drops, causing sinks and short shots; too much wastes Barrel Residence Time and risks resin degradation.
How do I calculate resin cost per part including the runner? Add part weight and runner weight, divide the runner across the number of cavities, then multiply by resin price per pound. The Resin Cost Per Part calculator combines Plastic Part Weight and Runner Weight with material cost, so a 40-gram part with 8 grams of runner per cavity at 1.20 dollars per pound runs about 0.127 dollars. A cold runner adds real cost, which is why Regrind Percentage and Plastic Regrind Savings matter on high-runner parts.
How long do I need to dry a hygroscopic resin? Drying time depends on the resin and target moisture: nylon and PET often need 4 to 6 hours at 175 to 180 F, while ABS may need 2 to 4 hours at 80 C. The Resin Drying Time calculator sets time from resin and throughput, and Resin Dryer Capacity confirms the dryer and Hopper Residence Time keep pace with the press. Molding wet nylon or PET causes splay, brittleness, and hydrolytic degradation that no process tweak fixes.

Last reviewed 2026-05-12.