Cryptosporidium and Giardia typically range in size from which of the following?

• A. 2 to 8 microns
• B. 3 to 15 microns
• C. 5 to 18 microns
• D. 7 to 20 microns

Answer: (B)

Understanding size helps explain how these parasites are removed by treatment processes. Cryptosporidium oocysts are about 4–6 microns, while Giardia cysts are roughly 8–12 microns in diameter. When you consider both organisms together, a practical range to capture their sizes is about 3–15 microns. This span covers the smaller Cryptosporidium and the larger Giardia cysts, supporting effective filtration and removal planning.

Other ranges miss part of this spectrum: too small a lower limit misses Giardia’s larger cysts, while too large upper limits extend beyond the typical sizes and don’t reflect the true overlap. So 3 to 15 microns best fits the combined size range of these protozoa.