Cover Page - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Nov. 23, 2020	Mar. 31, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--09-30
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Registrant Name	Twist Bioscience Corp
Entity Central Index Key	0001581280
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Security Exchange Name	NASDAQ
Entity Address, State or Province	CA
Title of 12(b) Security	Common Stock
Trading Symbol	TWST
Entity Common Stock, Shares Outstanding		45,152,511
Entity Incorporation, State or Country Code	DE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 1,088