Document and Entity Information - shares	3 Months Ended
	Jul. 31, 2020	Aug. 31, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jul. 31, 2020
Entity File Number	001-37784
Entity Registrant Name	GMS INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-2931287
Entity Address, Address Line One	100 Crescent Centre Parkway, Suite 800
Entity Address, City or Town	Tucker
Entity Address, State or Province	GA
Entity Address, Postal Zip Code	30084
City Area Code	800
Local Phone Number	392-4619
Title of 12(b) Security	Common Stock
Trading Symbol	GMS
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		42,735,602
Entity Central Index Key	0001600438
Current Fiscal Year End Date	--04-30
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false