About 2.2-2.4 kg.
This is similar to a dish that the gorgeous folk at Fred's restaurant do with the lamb we supply them. We tunnel-bone the leg leaving just the shank. Then we lather the inside with our delicious, home-made salsa verde sauce and roll it up and tie it. The good folk at Fred's cook it hanging over their open fire a la ficelle.
You may not be going to Fred's and you may not have an open fire in your kitchen but you can still roast a damn fine lamb leg and feast like a boss.