Do closets need a mezuzah?
The Pischei Teshuva 286:11 writes that a closet smaller than 4 by 4 amos requires a mezuzah. It is proper (as a chumrah *stringency) to place mezuzahs on closets provided one can walk into them. Rabbi Moshe Weiner (a Chabad Posek from Jerusalem) wrote: "Since a closet is actually an "otzar" a room that although not for dwelling, it is a place a person keeps his needs, and we pasken that otzarot are chayov, and any room part of the house should have a mezuza even if the size is less than 4x4 amos. Therefore in any case they should have a mezuza, however, no bracha is recited on rooms less than 4x4 amos".
I asked Rav Weiner if he agrees that that a closet smaller than 4 by 4 is merely a stringency or an actual obligation like other livable rooms of the house? This is his answer:"I would say it is between a chumra (stingency) and din (conventional law), because it involves 2 issues a small room less than 4x4 inside a house, and also
a otzar (storage room) - so it is hallachicaly something like a sfek-sfeka (double doubt). Still one should be careful to put a mezuza there.
Rabbi Levy Yitzchak Raskin(Dayan of Lubavitch community of London)wrote on this issue,"AS (Chabad)CHASSIDIM, WE ARE INCLINED 'LIFNIM MISHURAS HADIN'. AS SUCH, I DO FOLLOW THIS CHUMRA, PROVIDED THAT IT IS A WALK-IN CLOSET.
I will note that many Rabbonim are more lenient with closets and do not instruct the placing of a mezzuzah on a closet if it is less than 4 by 4 amos, however if it does reach that size all opinions require a mezuzah.
Concerning measuring the size (in order to make a bracha if it is at least 4 by 4 amos i.e. 37 square feet), how do we measure the closet space? do we only consider the non taken up closet space as part of the 4 by 4 or even the space which is taken up by shelves?
Rabbi Levy Yitzchak Raskin responded: "REGARDING MEASUREMENTS [FOR SAYING A BROCHO] - IT IS MISTAVER THAT FURNITURE THAT ENABLES THE USE OF THE ROOM SHOULD NOT DETRACT FROM ITS MEASUREMENTS. WOULD ANYONE SUGGEST THAT A BED DIMINISHES THE SIZE OF A SMALL 4X4 BEDROOM?" Later I found from the Shulchan Aruch HaRav 358:? which shows this idea in the same context regarding the measuring of space (for the laws of erecting an eruv).