I would like to know how many kgs do I need to be in order to get my breasts reduced?

Candidates for breast reduction will typically have documented evidence of neck/back and shoulder pain as well as rashes and bra strap grooving attributable to the increased breast weight. They will often demonstrate that these symptoms have been resistant to more conservative measures like therapy, weight loss and pharmacologic intervention. This is needed for insurance coverage.
In addition to establishing a case for medical necessity, there are also requirements for resection weight (when covered by insurance). This may be a standard "500 gm per side" stipulation or a more variable standard based upon body surface area/Schnur scale.
Insurance coverage is contingent on the meeting the requirements (which will vary) for establishing a case for medical necessity.
With regards to your specific question, it is not typically a question of weight but rather body surface area as it relates to breast size.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).
Donovan Rosas MD
Board Certified by the American Board of Plastic Surgery
Member: American Society for Aesthetic Plastic Surgery, American Society of Plastic Surgeons
RealSelf Verified Member
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The weight of breast tissue a plastic surgeon believes he or she can remove during a breast reduction generally varies between 400 and 600 grams. With a BMI over 35, reaching within 10 pounds of your goal weight over a period of several months prior to surgery would lower the risks of complications during and after surgery and enhance results. A Skype or in-office consultation with a board certified PS would be required to verify your candidacy.

Thank you for your question! It is hard to tell without a physical examination of exactly whats going on.  I suggest you seek a board certified plastic surgeon and have a consultation.  Best of luck!Dr Dhaval Patel 
Plastic Surgeon 
Double Board Certified 
Chicago
Hoffman Estates 
Oakbrook 
Orland Park