| Cover | 12 Months Ended |
| Mar. 31, 2023 | |
| Cover [Abstract] | |
| Document Type | 8-K |
| Entity File Number | 001-39675 |
| Document Period End Date | Jan. 31, 2023 |
| Entity Registrant Name | ALLEGRO MICROSYSTEMS, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 46-2405937 |
| Entity Address, Address Line One | 955 Perimeter Road |
| Entity Address, City or Town | Manchester, |
| Entity Address, State or Province | NH |
| Entity Address, Postal Zip Code | 03103 |
| City Area Code | (603) |
| Local Phone Number | 626-2300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | ALGM |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000866291 |
| Amendment Flag | false |
