| Cover Page | Aug. 20, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Aug. 20, 2021 |
| Entity Registrant Name | ThredUp Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-40249 |
| Entity Tax Identification Number | 26-4009181 |
| Entity Address, Address Line One | 969 Broadway |
| Entity Address, Address Line Two | Suite 200 |
| Entity Address, City or Town | Oakland |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94607 |
| City Area Code | 415 |
| Local Phone Number | 402-5202 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Common Stock, par value $0.0001 per share |
| Trading Symbol | TDUP |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Amendment Flag | false |
| Entity Central Index Key | 0001484778 |
| Entity Ex Transition Period | false |
