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Cover - USD ($)
$ in Millions
 12 Months Ended
Dec. 28, 2024
Feb. 14, 2025
Jun. 29, 2024
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 28, 2024    
Current Fiscal Year End Date --12-28    
Document Transition Report false    
Entity File Number 000-50307    
Entity Registrant Name FormFactor, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 13-3711155    
Entity Address, State or Province 7005 Southfront Road    
Entity Address, City or Town Livermore    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 94551    
City Area Code 925    
Local Phone Number 290-4000    
Title of 12(b) Security Common stock, $0.001 par value    
Trading Symbol FORM    
Security Exchange Name NASDAQ    
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    
Document Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 3,338.4
Entity Common Stock, Shares Outstanding (in shares)   77,565,827  
Documents Incorporated by Reference
Portions of the registrant's definitive Proxy Statement for the 2025 Annual Meeting of Stockholders, which will be filed within 120 days of the end of the registrant's fiscal year ended December 28, 2024, are incorporated by reference in Part III hereof. Except with respect to information specifically incorporated by reference in this Annual Report on Form 10-K, the Proxy Statement is not deemed to be filed as a part of this Annual Report on Form 10-K.
    
Entity Central Index Key 0001039399    
Amendment Flag false    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY