How do you calculate mold cavitation?

Divide available press hours by cycle time to get annual shots, then divide annual demand by that shot count and round up. With 6,000 hours and a 25-second cycle you get roughly 864,000 shots, so 2,000,000 parts needs about 3 cavities.

What is a good number of mold cavities?

Cavity counts are almost always powers of two or natural-balance layouts (1, 2, 4, 8, 16, 32) so the runner system fills evenly. Pick the smallest balanced count that clears your demand; running a 4-cavity tool when 3 cavities suffice keeps fill balanced.

How does cycle time affect cavitation?

Cycle time is the biggest lever. Halving a 25-second cycle to 12.5 seconds doubles your shots per year, which can let one fewer cavity carry the same annual volume and shrink the required mold and press.

Single cavity vs multi-cavity mold?

Single-cavity tools are cheaper, easier to fill, and ideal for low volume or large parts. Multi-cavity tools cut per-part cost at high volume but cost more, demand tighter runner balancing, and amplify any one cavity's defect across the shot.

Why round cavity count up?

You can't cut a fraction of a cavity, and rounding down would leave you short of demand. If the math says 2.4 cavities you need 3, then usually step to the next balanced layout of 4.

What press hours should I use?

Use realistic available hours, not calendar hours. Subtract planned maintenance, changeovers, and your shift pattern; a single-shift 6,000 hr year is very different from a 24/7 8,400 hr year and changes the cavity count directly.

Injection Molding calculator

Mold Cavitation Calculator

Mold cavitation is the number of identical cavities cut into an injection mold so that one shot ejects multiple parts at once. Tooling engineers and program managers size cavitation early in a part launch because it sets the press tonnage, the mold cost, and whether a single tool can keep up with the customer's annual volume. Get it wrong on the low side and you run a second shift or buy a second mold; too high and you overspend on tooling and tie up a larger press than the job needs. This calculator converts annual demand and machine availability into the minimum cavity count you must cut.

What this calculator does

Determine the optimal number of mold cavities from annual demand, available press cycle time, and production hours.
Use this when deciding how many cavities to cut in a new mold. Balance tooling cost against required production output and available press time.
It computes the minimum number of mold cavities required to meet annual part demand given your usable press hours and cycle time per shot.

Formula used

Shots per year = Available hours x 3600 / Cycle time
Minimum cavities = Annual demand / Shots per year (round up)

Inputs explained

Annual part demand: Total number of parts needed per year from customer forecasts or production plan.
Available production hours per year: Net press hours available after planned maintenance, holidays, and changeovers. Typical: 5,000 to 7,000 hrs.
Cycle time per shot: Full cycle time from mold close to mold open (injection, pack, cool, open, eject). Typical: 10 to 60 sec.

How to use the result

Use it during quoting and tool design, before you commit to an 8-, 16-, or 32-cavity mold, and again when demand forecasts change.
It assumes every cavity fills and ejects a good part every cycle; it does not subtract scrap, color changes, mold maintenance downtime, or the runner balance issues that get worse as cavity count rises.

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 cavitation? Divide available press hours by cycle time to get annual shots, then divide annual demand by that shot count and round up. With 6,000 hours and a 25-second cycle you get roughly 864,000 shots, so 2,000,000 parts needs about 3 cavities.
What is a good number of mold cavities? Cavity counts are almost always powers of two or natural-balance layouts (1, 2, 4, 8, 16, 32) so the runner system fills evenly. Pick the smallest balanced count that clears your demand; running a 4-cavity tool when 3 cavities suffice keeps fill balanced.
How does cycle time affect cavitation? Cycle time is the biggest lever. Halving a 25-second cycle to 12.5 seconds doubles your shots per year, which can let one fewer cavity carry the same annual volume and shrink the required mold and press.
Single cavity vs multi-cavity mold? Single-cavity tools are cheaper, easier to fill, and ideal for low volume or large parts. Multi-cavity tools cut per-part cost at high volume but cost more, demand tighter runner balancing, and amplify any one cavity's defect across the shot.
Why round cavity count up? You can't cut a fraction of a cavity, and rounding down would leave you short of demand. If the math says 2.4 cavities you need 3, then usually step to the next balanced layout of 4.

Last reviewed 2026-05-12.