| Cover | Jan. 06, 2025 |
| Cover [Abstract] | |
| Document Type | S-3/A |
| Amendment Flag | false |
| Entity Registrant Name | FOCUS UNIVERSAL INC. |
| Entity Central Index Key | 0001590418 |
| Entity Tax Identification Number | 46-3355876 |
| Entity Incorporation, State or Country Code | NV |
| Entity Address, Address Line One | 2311 East Locust Court |
| Entity Address, City or Town | Ontario |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 91761 |
| City Area Code | (626) |
| Local Phone Number | 272-3883 |
| Entity Filer Category | Non-accelerated Filer |
| Entity Small Business | true |
| Entity Emerging Growth Company | false |
