Document and Entity Information	9 Months Ended
	Oct. 01, 2011	Nov. 02, 2011
Entity Information [Line Items]
Entity Registrant Name	NANOMETRICS INC
Entity Central Index Key	0000704532
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Oct. 01, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		23,064,792