How do you calculate mold capacity per shift?

Multiply good parts per cycle by available cycles for gross capacity, then multiply by uptime and yield. With 4 parts/cycle, 480 cycles, 90% uptime and 97% yield, good output is 1,676 parts.

What's the difference between gross and good capacity?

Gross capacity is parts per cycle times cycles — 1,920 in the example. Good capacity applies uptime and yield losses, dropping it to 1,676 usable parts after 192 lost to downtime and about 52 to yield.

What is a realistic uptime for a rotomolding machine?

Well-run independent-arm machines often hold 85-92% uptime across a shift. The 90% used here costs 192 parts to downtime, which is why loading and index efficiency matter so much.

How does yield affect shift capacity?

Yield trims the parts that survive after downtime losses. At 97% first-pass yield on this run, roughly 52 parts are lost to warpage, voids, or thin walls even though the machine ran.

How can I increase parts per shift?

Raise parts per cycle with more or larger molds, add cycles by shortening index and cure time, and lift uptime and yield by cutting jams, mis-loads, and reject-causing defects.

Why use both uptime and yield instead of one factor?

They measure different losses — uptime is time the machine ran, yield is the fraction of molded parts that pass. Separating them tells you whether to attack downtime or defects first.

Rotational Molding calculator

Mold Capacity Per Shift Calculator

Mold Capacity Per Shift estimates how many good parts a rotomolding machine can actually deliver in a shift, not just in theory. It starts from parts per oven cycle and the number of cycles available, then discounts for machine uptime and first-pass yield so the answer reflects real losses to breakdowns, index waits, warpage, and voids. Schedulers and production planners use it to set achievable shift targets and to spot whether uptime or yield is the bigger drag on output.

What this calculator does

Mold Capacity Per Shift estimates how many good parts a rotomolding machine can actually deliver in a shift, not just in theory.
Use it when mold capacity per shift in rotational molding is being asked to take on more work and you need to know if there is room.
It computes gross capacity from parts per cycle and available cycles, then multiplies by uptime and yield to get good-part output.

Formula used

Gross mold capacity per shift capacity = units per cycle × available cycles
Good capacity = gross capacity × uptime × yield

Inputs explained

Good parts per oven cycle:
Available oven cycles per shift:
Machine uptime:
First-pass yield:

How to use the result

Use it when building a shift schedule or committing a delivery date for a rotomolded part.
It assumes a steady cycle time; a heavy or thick-walled part with a longer oven cycle reduces available cycles and must be reflected in the inputs.

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 capacity per shift? Multiply good parts per cycle by available cycles for gross capacity, then multiply by uptime and yield. With 4 parts/cycle, 480 cycles, 90% uptime and 97% yield, good output is 1,676 parts.
What's the difference between gross and good capacity? Gross capacity is parts per cycle times cycles — 1,920 in the example. Good capacity applies uptime and yield losses, dropping it to 1,676 usable parts after 192 lost to downtime and about 52 to yield.
What is a realistic uptime for a rotomolding machine? Well-run independent-arm machines often hold 85-92% uptime across a shift. The 90% used here costs 192 parts to downtime, which is why loading and index efficiency matter so much.
How does yield affect shift capacity? Yield trims the parts that survive after downtime losses. At 97% first-pass yield on this run, roughly 52 parts are lost to warpage, voids, or thin walls even though the machine ran.
How can I increase parts per shift? Raise parts per cycle with more or larger molds, add cycles by shortening index and cure time, and lift uptime and yield by cutting jams, mis-loads, and reject-causing defects.

Last reviewed 2026-05-12.