Document and Entity Information - shares	3 Months Ended
	Apr. 01, 2022	Apr. 29, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Apr. 01, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Entity Registrant Name	EXPONENT, INC.
Entity Central Index Key	0000851520
Current Fiscal Year End Date	--12-30
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Trading Symbol	EXPO
Entity Common Stock, Shares Outstanding		51,821,607
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity File Number	0-18655
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	77-0218904
Entity Address, Address Line One	149 COMMONWEALTH DRIVE
Entity Address, City or Town	MENLO PARK
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94025
City Area Code	650
Local Phone Number	326-9400
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of each class	Common Stock, par value $0.001 per share
Name of each exchange on which registered	NASDAQ