| Cover | Sep. 02, 2021 | Aug. 04, 2021 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Nov. 15, 2021 | |
| Entity Registrant Name | Keros Therapeutics, Inc. | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 001-39264 | |
| Entity Tax Identification Number | 81-1173868 | |
| Entity Address, Address Line One | 99 Hayden Avenue | |
| Entity Address, Address Line Two | Suite 120 | |
| Entity Address, Address Line Three | Building E | |
| Entity Address, City or Town | Lexington | |
| Entity Address, State or Province | MA | |
| Entity Address, Postal Zip Code | 02421 | |
| City Area Code | 617 | |
| Local Phone Number | 314-6297 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share | |
| Trading Symbol | KROS | |
| Security Exchange Name | NASDAQ | |
| Entity Emerging Growth Company | true | |
| Entity Ex Transition Period | false | |
| Entity Central Index Key | 0001664710 | |
| Amendment Flag | false |
