Flat Iron vs Outside Round — What's the Difference?
Quick Answer
Flat Iron (flat iron steak) and Outside Round (bottom round (outside round)) are not the same cut: Flat Iron is chuck primal (Infraspinatus muscle, top blade of the shoulder clod); Outside Round is round primal (Outer thigh of the hindquarter).
Canonical entities: Flat Iron · Outside Round
Side-by-side
| flat iron | outside round | |
|---|---|---|
| Primal | chuck | round |
| Muscle / location | Infraspinatus muscle, top blade of the shoulder clod | Outer thigh of the hindquarter |
| 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. | From the outer thigh (biceps femoris). Leaner and less tender than inside round. Used for roasts, rouladen, and ground beef. Often sold as bottom round roast or eye of round. |
Key differences
- Different primals: chuck vs round.
- 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.
Outside Round
Pick Outside Round when its primal/muscle traits fit the dish: From the outer thigh (biceps femoris). Leaner and less tender than inside round. Used for roasts, rouladen, and ground beef. Often sold as bottom round roast or eye of round.
Flat Iron and Outside Round are different canonical muscles/primals: Flat Iron is chuck (Infraspinatus muscle, top blade of the shoulder clod); Outside Round is round (Outer thigh of the hindquarter).
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) · outside round (what-is) · flat iron hub · outside round hub