And one more way to look at it: Half Bottle: 375 milliliters Standard Bottle: (standard size) 750 milliliters Magnum: 1.5 liters or the equivalent of two standard bottles. Double Magnum: 3liters, or the equivalent of four standard bottles Jeroboam: 4.5 liters, or the equivalent of six standard bottles (Note: in the case of sparkling wine, a jeroboam will contain 3 liters, or the equivalent of four standard bottles.) Rehoboam: Same as Jeroboam, but a different bottle shape. Imperial: 6liters, or the equivalent of eight standard bottles. Methuselah: Same as Imperial, but a different bottle shape. Salmanazar: 9liters, or the equivalent of twelve bottles Nebuchadnezzar: 12 to16 liters (varies,) or the equivalent of fourteen to twenty standard bottles. Melchior: 18 liters, or the equivalent of twenty- four standard bottles. Case: 12 standard bottles (bottles must be from a single winery, but may be mixed in vintage year and varietals) Magnum Case: 6magnums (nine liters) or the equivalent of twelve standard bottles. Barrel: 180 liters, or the equivalent of 240 standard bottles (20 cases.)
I heard European legislation changed somewhere along the line. 75cl was always the intended volume, but it used to be the case that that the actual volume could never be less than the volume on the label, so producers used a lower number on the label to make sure they were legal. Now, legally, the volume on the label is the average volume in a bottle. There must also be some maximum allowable variation, but with automatic bottling lines volumes are presumably pretty accurate these days. Not 100% sure about all that - I emphasise the “I heard” bit. But now you have read it on the internet, so it must be pretty close to being a fact now