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Document and Entity Information - USD ($)
 12 Months Ended
Apr. 30, 2021
Jul. 15, 2021
Oct. 31, 2020
Document And Entity Information      
Entity Registrant Name Ocean Power Technologies, Inc.    
Entity Central Index Key 0001378140    
Document Type 10-K    
Document Period End Date Apr. 30, 2021    
Amendment Flag false    
Current Fiscal Year End Date --04-30    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filer No    
Entity's Reporting Status Current Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business Flag true    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 40,800,000
Entity Common Stock, Shares Outstanding   52,458,011  
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2021