Cover - shares	9 Months Ended
	Sep. 30, 2021	Oct. 31, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-39748
Entity Registrant Name	PUBMATIC, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5863224
Entity Address, Address Line One	3 Lagoon Drive
Entity Address, Address Line Two	Suite 180
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94065
Title of 12(b) Security	Class A common stock, $0.0001 par value per share
Trading Symbol	PUBM
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Amendment Flag	false
Entity Central Index Key	0001422930
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		27,545,541
Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		23,760,497