Flat Iron vs Tenderloin — What's the Difference?
Quick Answer
Flat Iron (flat iron steak) and Tenderloin (beef tenderloin) are not the same cut: Flat Iron is chuck primal (Infraspinatus muscle, top blade of the shoulder clod); Tenderloin is loin primal (psoas major).
Canonical entities: Flat Iron · Tenderloin
Side-by-side
| flat iron | tenderloin | |
|---|---|---|
| Primal | chuck | loin |
| Muscle / location | Infraspinatus muscle, top blade of the shoulder clod | psoas major |
| Character | The second most tender muscle on the entire animal, after the tenderloin. A flat, rectangular steak extracted from the top blade by splitting it along the central connective tissue. Uniform thickness makes it ideal for grilling. Also known as butler's steak in the UK. | Most tender muscle of the loin; center cuts often sold as filet mignon. |
Key differences
- Different primals: chuck vs loin.
- Texture and slicing: compare fibrous, grain-heavy cuts vs more tender steak-style muscles based on each cut’s description.
- Retail naming diverges by country—always map through a canonical cut when translating menus or labels.
When to use each
Flat Iron
Pick Flat Iron when you want its specific marbling/texture profile: The second most tender muscle on the entire animal, after the tenderloin. A flat, rectangular steak extracted from the top blade by splitting it along the central connective tissue. Uniform thickness makes it ideal for grilling. Also known as butler's steak in the UK.
Tenderloin
Pick Tenderloin when its primal/muscle traits fit the dish: Most tender muscle of the loin; center cuts often sold as filet mignon.
Flat Iron and Tenderloin are different canonical muscles/primals: Flat Iron is chuck (Infraspinatus muscle, top blade of the shoulder clod); Tenderloin is loin (psoas major).
Choose based on tenderness, marbling, grain direction, and how you plan to cook (sear vs braise vs slice thin).
Read the full guides: flat iron (what-is) · tenderloin (what-is) · flat iron hub · tenderloin hub