Rashi on Leviticus 27:25/רש"י על ויקרא כ״ז:כ״ה

1וכל ערכך יהיה בשקל הקדש Every valuation shall be made according to the holy shekel: i.e., every valuation regarding which shekels are written, will be made according to the holy shekel.

2עשרים גרה TWENTY GERAH — twenty meahs. This was what it was originally, but later on they increased it by one sixth. Our Rabbis stated: six silver meahs make a silver denar; thus twenty-four meahs make a selah (a shekel) (cf. Rashi on Exodus 30:13), a shekel being four denars (Bekhorot 26b).