Cover Page - USD ($)	12 Months Ended
	Sep. 30, 2025	Nov. 11, 2025	Mar. 31, 2025
Cover [Abstract]
City Area Code	314
Local Phone Number	644-7600
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	BRBR
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 9,367,938,437
Entity Common Stock, Shares Outstanding		119,672,080
Documents Incorporated by Reference	Certain portions of the registrant’s definitive proxy statement for its 2026 annual meeting of stockholders, to be filed with the Securities and Exchange Commission within 120 days after September 30, 2025, are incorporated by reference into Part III of this report.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2025
Document Fiscal Year Focus	2025
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--09-30
Document Transition Report	false
Amendment Flag	false
Entity File Number	1-39093
Entity Registrant Name	BellRing Brands, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	87-3296749
Entity Central Index Key	0001772016
Entity Address, Address Line One	2503 S. Hanley Road
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63144
Document Financial Statement Error Correction [Flag]	false