Where do I find the drying air needed per kg?

The dryer maker's material table. Wittmann lists 1.72 m³/kg for PBT, 1.34 for PC and 2.11 for nylon 66. The common rule of 1 cfm per lb/hr equals 3.75 m³/kg, a more generous figure.

Why is my dryer hopper limited when it has spare air?

Each pellet must spend the full drying time in the hopper, so the hopper can release at most its contents divided by that time each hour. Extra air cannot shorten the supplier's time at temperature.

Is an oversized dryer a problem?

It can be. Conair notes too much air wastes energy and raises return air temperature, weakening the desiccant. Novatec advises giving the maker your lowest throughput too, so resin is not over-dried.

Why does switching resin change capacity on the same dryer?

Each resin needs its own air per kg, drying time and bulk density. With Wittmann's figures, this 100 L, 60 m³/h dryer handles 23.1 kg/hr of PBT, 24.0 of PC and 22.7 of nylon 66.

Injection Molding calculator

Resin Dryer Capacity Calculator

Find the rate a dryer can deliver on this resin, set by its air output and hopper, and whether your presses exceed it. You need the spec sheet, the maker's air figure and the drying time.

What this calculator does

The kg/hr a dryer and its hopper can dry for your resin, against what every press it feeds consumes.

Formula used

Airflow limit (kg/hr) = dryer process air output ÷ drying air needed per kg
Hopper limit (kg/hr) = hopper working volume × bulk density ÷ supplier drying time
Dryer capacity = MIN(airflow limit, hopper limit)
Dryer load = total consumption ÷ dryer capacity × 100; headroom = capacity − consumption
Air output needed = consumption × air per kg; hopper volume needed = consumption × drying time ÷ bulk density

Inputs explained

Total Resin Consumption Across All Presses: Sum of every press fed: g per shot × shots/hr ÷ 1,000.
Dryer Process Air Output: From the dryer spec sheet; 1 cfm is 1.699 m³/h.
Drying Air Needed per Kg: For this resin, from the dryer maker's material table.
Drying Hopper Working Volume: Volume below the loader's fill level, from the hopper spec sheet.
Resin Bulk Density: Pellet bulk density from the resin or dryer maker's table.
Supplier Drying Time: Hours at drying temperature and dew point, from the resin datasheet.

How to use the result

Best suited to adding a press to an existing dryer, switching a dryer to another resin, specifying a dryer for a new cell.
Does not check heater power, desiccant condition or dew point under load. Does not flag a dryer too large for the load, which can over-dry resin at low rates.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 280.569 (BLS, Aug 2026), up 6.6% 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

Where do I find the drying air needed per kg? The dryer maker's material table. Wittmann lists 1.72 m³/kg for PBT, 1.34 for PC and 2.11 for nylon 66. The common rule of 1 cfm per lb/hr equals 3.75 m³/kg, a more generous figure.
Why is my dryer hopper limited when it has spare air? Each pellet must spend the full drying time in the hopper, so the hopper can release at most its contents divided by that time each hour. Extra air cannot shorten the supplier's time at temperature.
Is an oversized dryer a problem? It can be. Conair notes too much air wastes energy and raises return air temperature, weakening the desiccant. Novatec advises giving the maker your lowest throughput too, so resin is not over-dried.
Why does switching resin change capacity on the same dryer? Each resin needs its own air per kg, drying time and bulk density. With Wittmann's figures, this 100 L, 60 m³/h dryer handles 23.1 kg/hr of PBT, 24.0 of PC and 22.7 of nylon 66.

Last reviewed 2026-10-01.