- The ketem must be bigger than a gris. Only parts of the ketem which are halachically red are included in the gris. Colors such as white, green or yellow are not included. A gris is about the area of a penny, no matter the shape of the stain. It is sometimes difficult to figure out how big a ketem is. When in doubt consult a rabbi.
- We do not combine ketamim found on clothing that are less than a gris. Only if a single ketem is bigger than a gris is a woman niddah.
- Ashkenazim do add up ketamim found on skin. If there are a few ketamim, each smaller than a gris, but they combine to be bigger than a gris, Ashkenazim will consider that a ketem which makes a woman a niddah.
Halacha » Gris – Size of the Ketem