| Document And Entity Information | Aug. 11, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 11, 2022 |
| Entity Registrant Name | Erasca, Inc. |
| Entity Central Index Key | 0001761918 |
| Entity Emerging Growth Company | true |
| Entity File Number | 001-40602 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 83-1217027 |
| Entity Address, Address Line One | 3115 Merryfield Row |
| Entity Address, Address Line Two | Suite 300 |
| Entity Address, City or Town | San Diego |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92121 |
| City Area Code | (858) |
| Local Phone Number | 465-6511 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Ex Transition Period | false |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Trading Symbol | ERAS |
| Security Exchange Name | NASDAQ |
