Document and Entity Information - shares	3 Months Ended
	Nov. 28, 2020	Jan. 04, 2021
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Nov. 28, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	UNIFIRST CORPORATION
Entity Central Index Key	0000717954
Current Fiscal Year End Date	--08-28
Entity Filer Category	Large Accelerated Filer
Title of 12(b) Security	Common Stock, $0.10 par value per share
Trading Symbol	UNF
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity File Number	001-08504
Entity Tax Identification Number	04-2103460
Entity Address, Address Line One	68 Jonspin Road
Entity Address, City or Town	Wilmington
Entity Address, State or Province	MA
Entity Incorporation, State or Country Code	MA
Entity Address, Postal Zip Code	01887
City Area Code	(978)
Local Phone Number	658-8888
Document Quarterly Report	true
Document Transition Report	false
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,214,959
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,643,009