How much is a Peruta?
The Peruta was the smallest form of currency in the times of the Mishna and Talmud. It was a copper coin. Its silver worth is the weight of half a barley which is about .025 grams. Thus, the worth of a Peruta is 0.025 of a gram of silver [1/40th of a gram]. In accordance to the current price of silver [$0.54 per gram-January 2017] the worth of a Peruta is 1.35 cents or 6 [5.1] Agurot. One must periodically verify anew as to the worth of silver, in order to know the current price of a Peruta. Some Rabbanim of today hold that one must also include the amount of sales tax levied on purchasing this amount of silver in his country [i.e. 17% in Israel, in U.S.A. depends on your state].
Areas in Halacha that a Peruta is relevant:
In Halacha, less than a Peruta is not considered money, and a value dependent Mitzvah cannot be fulfilled when using less than a Peruta. The following are some areas in Halacha in which a Peruta’s worth is relevant.
- Tzedaka: One who is careful to give money to charity each day prior to Davening is to give at least a Peruta’s worth. The same applies prior to candle lighting.
- Matanos Laevyonim: The minimum value one must give a pauper to fulfill the Mitzvah of Matanos Laevyonim is a Peruta.
- Pidyon Maaser Sheiyni: Maaser Sheiyni is redeemed onto a Peruta.
- Kiddushin: One may only marry a woman with an item worth a Peruta or more. If the item is worth less than a Peruta she remains single.
- Moda Bemiktzas: One who admits to a partial claim is only liable for a swear if he admitted to being liable for at least a Peruta’s worth.
 Shiurei Torah 3/42
 Shiureiy Torah ibid in name of Rambam; Rif; Ran in name of Geonim; Rabbeinu Chananel Shavuos 39b; Rosh Bechoros 8; Michaber Y.D. 331/133; E.H. 27; C.M. 88
 See Igros Kodesh 11/18 “A Peruta or two” [printed in Shulchan Menachem 1/151]
 Ritva Megillah brought in M”B 694/2; Kaf Hachaim 694/7; See Ashel Avraham Butchach 695; The Peri Megadim [brought in M”B 694/2] writes he has not found an amount written anywhere.
 Michaber Y.D. 131/133
 Michaber E.H. 31/1
 Michaber C.M. 88/1