Document and Entity Information - shares	9 Months Ended
	Sep. 26, 2015	Oct. 23, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	NANOMETRICS INC
Entity Central Index Key	0000704532
Document Type	10-Q
Document Period End Date	Sep. 26, 2015
Amendment Flag	false
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-26
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		24,188,234
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes