TT #277 · Parshas Tazria · Aliyah 7 · Passuk 51
English: The priest shall examine the lesion on the seventh day; if it has spread in the garment, warp or woof, or leather article, the lesion is malignant tzaraas; it is impure.
Torah Temimah cites Sifra (Toras Kohanim) for the gris-sized minimum measure for a newly counted garment lesion.
Sifra — Vayikra 13, Midrash Sefer
English: Might any amount count? The Sifra compares the word “lesion” here with the lesion on skin and derives the minimum measure of a gris.
Textual derivation
Do not confuse the measure of spread with the measure of a separate lesion: adjacent spread may be any amount, but a newly counted lesion must reach a gris.