An adult female of S. coffeae has a hemispherical form with a smooth surface. The colour is usually dark to sometimes lighter brown or almost yellow, with many evenly distributed light yellow flecks. The high, rounded form and smooth surface distinguish the species from most other soft scales. The size depends on the host plant and can vary from 2 to 4.5 mm.
The young nymphs are white to yellowish, more oval in form and with a raised H-pattern on the dorsal surface. All instars live on the underside of leaves, often close to the midrib. Only when an infestation is particularly severe do individual scales appear on stems, branches and twigs.