Document And Entity Information - shares	6 Months Ended
	Oct. 31, 2020	Dec. 11, 2020
Document Information [Line Items]
Entity Registrant Name	BUTLER NATIONAL CORP
Entity Central Index Key	0000015847
Trading Symbol	buks
Current Fiscal Year End Date	--04-30
Entity Filer Category	Non-accelerated Filer
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding (in shares)		74,033,347
Entity Shell Company	false
Document Type	10-Q
Document Period End Date	Oct. 31, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
Title of 12(g) Security	Common Stock $.01 Par Value