| Document and Entity Information | May 18, 2021 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 5, 2022 |
| Entity File Number | 001-33264 |
| Entity Registrant Name | CARPARTS.COM, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 68-0623433 |
| Entity Address, Address Line One | 2050 W. 190th Street |
| Entity Address, Adress Line Two | Suite 400 |
| Entity Address, City or Town | Torrance |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 90504 |
| City Area Code | 424 |
| Local Phone Number | 702-1455 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | PRTS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001378950 |
| Amendment Flag | false |
