| Cover | Feb. 14, 2023 |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 14, 2023 |
| Entity File Number | 001-40230 |
| Entity Registrant Name | FORUM MERGER IV CORPORATION |
| Entity Central Index Key | 0001842916 |
| Entity Tax Identification Number | 86-1556509 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1615 South Congress Avenue |
| Entity Address, Address Line Two | Suite 103 |
| Entity Address, City or Town | Delray Beach |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 33445 |
| City Area Code | (212) |
| Local Phone Number | 739-7860 |
| Written Communications | false |
| Soliciting Material | true |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | false |
| Units, each consisting of one share of Class A common stock and one-fourth of one redeemable warrant | |
| Title of 12(b) Security | Units, each consisting of one share of Class A common stock and one-fourth of one redeemable warrant |
| Trading Symbol | FMIVU |
| Security Exchange Name | NASDAQ |
| Class A common stock, par value $0.0001 per share | |
| Title of 12(b) Security | Class A common stock, par value $0.0001 per share |
| Trading Symbol | FMIV |
| Security Exchange Name | NASDAQ |
| Warrants, each whole warrant exercisable for one share of Class A common stock, each at an exercise price of $11.50 per share | |
| Title of 12(b) Security | Warrants, each whole warrant exercisable for one share of Class A common stock, each at an exercise price of $11.50 per share |
| Trading Symbol | FMIVW |
| Security Exchange Name | NASDAQ |
