How Long to Grill a 1-Inch London Broil
About 10-12 minutes total over medium-high heat (around 450°F), flipping once halfway through — roughly 5-6 minutes per side. Pull the meat at 130-135°F internal for medium-rare, then rest 10 minutes before slicing thin against the grain.
What Is London Broil, and Why Marinate It First?
“London broil” usually refers to a cooking method applied to a lean, tougher cut — often top round or flank — rather than a specific cut on its own. Because it’s lean and has relatively coarse muscle fibers, it benefits a lot from marinating beforehand: the acid and enzymes in a marinade help tenderize the surface and add flavor that this cut doesn’t have much of naturally. Skipping the marinade is one of the fastest ways to end up with a tough result.
How to Grill London Broil Step by Step
Marinate
Marinate for at least 2 hours, or ideally overnight, in a mix of oil, acid (vinegar, citrus, or Worcestershire), and aromatics like garlic and herbs.
Preheat to Medium-High (400-450°F)
Heat your grill to medium-high, in the 400-450°F range.
Grill and Flip Once
Remove the meat from the marinade and pat it dry. Grill over direct heat, flipping once about halfway through the total cook time.
Rest and Slice Against the Grain
Rest for about 10 minutes, then slice thin, against the grain. This step matters more for London broil than almost any other cut on this site — slicing with the grain leaves long muscle fibers intact, and the meat will taste noticeably tougher even if it was cooked correctly.
Grilling at 400°F vs. 450°F
Both work for a 1-inch London broil. At 450°F, expect the full cook to land closer to 10 minutes; at 400°F, it’ll run a little longer — closer to 12-14 minutes — since the lower heat builds a crust more slowly. Either way, use a thermometer to confirm you’ve hit 130-135°F rather than relying on a fixed time, since actual thickness varies by cut.
What Is the 3-3-3 Rule? Does It Apply to London Broil?
The 3-3-3 rule (3 minutes per side direct heat, then 3 minutes indirect or resting) is aimed more at thicker steaks like ribeye than at a relatively thin, wide cut like London broil. For a 1-inch London broil, you’ll generally flip once rather than manage a separate indirect phase — so treat 3-3-3 as a rough reference from the steak world, not a literal recipe for this cut.
Common Mistakes Cooking London Broil
- Skipping the marinade. Without it, this lean cut is much more likely to come out tough and bland.
- Grilling past medium. London broil has very little fat to keep it moist once it’s overcooked — medium-rare to medium is the practical ceiling.
- Slicing with the grain instead of against it. This is the single biggest factor in how tender the final slices feel.
- Not resting the meat. Cutting in right away lets juices escape instead of settling back into the meat.
Prefer Low and Slow? Try Smoking It Instead
Grilling gives you a fast, hot cook, but if you’d rather use a smoker and a longer cook time, see our guide to smoking London broil for tenderness — it walks through a slower approach, including whether extra time actually helps tenderness on this cut.
FAQ
What is the 3-3-3 rule for grilling steak? Roughly 3 minutes per side over direct heat, then 3 minutes indirect or resting — more relevant to thicker steaks than to a relatively thin cut like London broil.
How long to grill a 1-inch steak at 400 degrees? Around 12-14 minutes total, flipping once, to reach 130-135°F for medium-rare — a bit longer than at 450°F.
Should I grill London broil with the lid open or closed? Closed, for consistent heat, since London broil cooks fast and benefits from steady, even temperature.
What are common mistakes cooking London broil? Skipping the marinade, cooking past medium, slicing with the grain instead of against it, and not resting before slicing.