Rump roast is a lean, hearty cut with bold beef flavor. It cooks beautifully when roasted slowly and sliced thin, making it perfect for classic roast beef dinners or sandwiches the next day.
 
Small Rump Roast- 3.25-3.5
Large Rump Roast- 3.5-3.75
 
Tender Slow Cooker Rump Roast - The Oregon Dietitian