| Document and Entity Information | Mar. 03, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 3, 2021 |
| Entity Registrant Name | ACME UNITED CORP |
| Entity Central Index Key | 0000002098 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-07698 |
| Entity Incorporation, State or Country Code | CT |
| Entity Tax Identification Number | 06-0236700 |
| Entity Address, Address Line One | 55 Walls Drive |
| Entity Address, City or Town | Fairfield |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06824 |
| City Area Code | 203 |
| Local Phone Number | 254-6060 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $2.50 par value per share |
| Trading Symbol | ACU |
| Security Exchange Name | NYSEAMER |
