| Document and Entity Information | Jan. 10, 2023 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 10, 2023 |
| Entity Registrant Name | RMG ACQUISITION CORP. III |
| Entity Incorporation, State or Country Code | E9 |
| Entity File Number | 001-40013 |
| Entity Tax Identification Number | 98-1574120 |
| Entity Address, Address Line One | 57 Ocean, Suite 403 |
| Entity Address, Address Line Two | 5775 Collins Avenue |
| Entity Address, City or Town | Miami Beach |
| Entity Address State Or Province | FL |
| Entity Address, Postal Zip Code | 33140 |
| City Area Code | 786 |
| Local Phone Number | 359-4103 |
| Written Communications | true |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001838108 |
| Amendment Flag | false |
| Units, each consisting of one Class A Ordinary Share, $0.0001 par value, and one-fifth of one redeemable warrant [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Units, each consisting of one Class A ordinary share and one-fifth of one redeemable warrant |
| Trading Symbol | RMGCU |
| Security Exchange Name | NASDAQ |
| Class A Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Class A ordinary shares included as part of the units |
| Trading Symbol | RMGC |
| Security Exchange Name | NASDAQ |
| Redeemable warrants included as part of the units [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Redeemable warrants included as part of the units |
| Trading Symbol | RMGCW |
| Security Exchange Name | NASDAQ |
