| Document and Entity Information | Feb. 16, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 16, 2022 |
| Entity File Number | 001-39513 |
| Entity Registrant Name | Outset Medical, Inc. |
| Entity Central Index Key | 0001484612 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 20-0514392 |
| Entity Address, Address Line One | 3052 Orchard Dr. |
| Entity Address, City or Town | San Jose |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 95134 |
| City Area Code | 669 |
| Local Phone Number | 231-8200 |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | OM |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
