Ryan Choi's abilities stand identical to that of his mentor and friend Ray Palmer, the original Atom. Having the capability to change size, mass, and weight at will through a dwarf star powered device known as the Quantum Bio-Belt, he can shrink down beyond the particle scale. This enables Ryan, in his own words, to miniaturize himself while retaining full physique at this level. Initially, he could only do so due to the belt his predecessor's enemy, Lady Chronos had made for him. But after time of using the senior physicist's invention, he eventually contracted odd microorganisms that bonded to his blood cells on a genetic level. These small matter-devouring creatures allowed him similar 100% bodily control over the molecular physiological structure as his science teacher. Essentially letting him grow or shrink without the need of a belt under his own willpower. As Ryan, he possesses expertise in physics.