Pore size and diameter: two different decisions

A filter's pore size (in µm) and its physical diameter (in mm) are independent specifications. A 0.22 µm pore is available in 13 mm, 25 mm, 47 mm, and other diameters—the pore rating stays the same; only the surface area and the hardware it fits change. Confusing "0.22" with "25 mm" (or vice versa) is a common source of ordering errors.

Common pore sizes and what they're generally used for

Pore rating	Common use
0.1–0.2 µm	Sterilizing-grade filtration (0.22 µm is the conventional benchmark for bacterial retention in many workflows)
0.45 µm	General clarification, sample prep ahead of HPLC/analytical instruments, removing fine particulate without removing dissolved analyte
0.8–1.2 µm	Coarse particulate removal, pre-filtration ahead of a tighter final filter
3–8 µm and larger	Cell harvesting, coarse debris removal, some environmental and microbiological sample prep

These are general, widely used conventions, not a guarantee for any specific product or method. Sterility, retention efficiency, and validated performance depend on the exact membrane and the method it's being used in—confirm against the product's own documentation for regulated or validated work.

Diameter follows sample volume and hardware

Smaller diameters (13 mm, 25 mm) suit small sample volumes and syringe-filter formats. Larger diameters (47 mm, 90 mm, 142 mm, 293 mm) suit vacuum filtration of larger volumes, where more surface area means less time spent waiting for a viscous or particulate-loaded sample to pass through. If a sample volume is large or slow to filter, increasing diameter—not just tightening or loosening the pore rating—is often the more effective fix.

Supported vs. unsupported membranes

Thin membranes used at higher pressure (syringe filtration, some vacuum setups) often need a supporting layer to resist rupture. Product listings that specify "supported" or include a support screen are built for that use; an unsupported membrane in a high-pressure format is a common cause of filter failure mid-run.

Working backward from the question you're answering

It helps to state the actual requirement before picking a number: "remove bacteria before this goes on media," "clarify this sample so it doesn't clog the column," "get particulate out without losing dissolved analyte." Each of those points to a different pore size, and often a different material—see our membrane material guide for the material side of that decision.