Document and Entity Information - shares	6 Months Ended
	Jun. 29, 2019	Jul. 26, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	NANOMETRICS INC
Entity Central Index Key	0000704532
Document Type	10-Q
Document Period End Date	Jun. 29, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	NANO
Current Fiscal Year End Date	--12-28
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.001 par value per share
Security Exchange Name	NASDAQ
Entity Address, State or Province	CA
Entity File Number	000-13470
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	1550 Buckeye Drive
Entity Address, City or Town	Milpitas
City Area Code	408
Local Phone Number	545-6000
Entity Address, Postal Zip Code	95035
Entity Tax Identification Number	94-2276314
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		24,828,384