Question: how many litres in a magnum bottle?
Answer: A “magnum” is 1.5 liters, or the equivalent of two bottles, and if you double that, you'd have a “double magnum,” at 3 liters. (A 3-liter bottle is also known as a “jeroboam” in Champagne and Burgundy, but in Bordeaux, a jeroboam is 4.5 liters.)