Double old fashioned vs old fashioned glass

Names in this category are loose and overlapping, which is most of why the question gets asked. The capacities are what to go on.

Both old fashioned glasses share the same design language - squat, wide mouth, heavy base - because both are built for a drink you stir in the glass over ice and then drink without a straw. The heavy base is not styling; it is what makes the glass stable when you muddle or stir in it and what gives it thermal mass.

Here is the arithmetic that settles the question. A 2-inch cube is 8 cubic inches, which is roughly 4.4 fluid ounces of displacement. A 60mm sphere is a little less, around 3.6 oz. Either way, a single large piece of ice occupies something like 40 to 50 percent of a 9 oz glass before any liquid goes in.

1. Single old fashioned, 9 oz, with a 2-inch cube: about 4.6 oz of usable volume. A 2 oz pour plus half an ounce of dilution fills most of it. Workable, visually full, and it will spill if you move briskly.
2. Double old fashioned, 12 oz, with a 2-inch cube: about 7.6 oz of usable volume. The same drink sits with clear freeboard and the cube has room to turn as it melts.
3. Single old fashioned, 9 oz, with three small cubes: fine. This is what the glass was sized for, back when nobody was making 2-inch rocks at home.

That last line is the real history of this question. The single old fashioned glass is correctly sized for mid-century bar ice. Large-format clear ice at home is recent, and the double old fashioned is the glass that accommodates it. Rocks glass size guide has the full capacity table, and best clear ice molds is where the 2-inch cube comes from.

A double old fashioned and a highball can have the same stated capacity and still be wrong for each other's drinks, because capacity is not the useful property - the aspect ratio is.

• A double old fashioned is wide and short. Large surface area, so aromatics reach your nose; room for one big cube; your hand wraps the glass. Right for spirit-forward drinks you sip slowly.
• A highball is narrow and tall. Small surface area, so carbonation lasts; a column of ice keeps the drink cold top to bottom; the drink stays long. Right for anything with soda in it.
• Swap them and both drinks suffer. A gin and tonic in a wide tumbler goes flat; an old fashioned in a highball has no aroma and the ice rattles down a tube.

So the useful question is not which glass is bigger, it is whether the drink is sipped or quenched. Cocktail glassware types names the shapes, and what glass for a Manhattan covers the up-serve case where neither of these glasses is correct.

Buy doubles. If you are buying one set of tumblers and you make old fashioneds, Negronis or drink whiskey on a rock, 12 oz is the capacity that works and 9 oz is the capacity that constrains you. A double old fashioned also serves perfectly well as a single - a neat pour in a 12 oz glass looks like a measured drink, not a mistake.

The case for owning singles as well is narrower but real: a neat pour, a short highball-free drink, or a glass to hand to someone who does not want a big drink. Two of each is a sensible home-bar split if you have the cupboard. Best glassware sets for a home bar covers the whole cupboard in order.

• Rim: a laser-cut rim is thinner against your mouth; a rolled rim is more durable. Libbey publish the Signature line as cut and chip resistant, which is the combination to look for.
• Base: heavy, for stability and thermal mass. A light tumbler tips when you stir in it.
• Mouth diameter: check it actually takes your ice. A 2-inch cube needs a mouth comfortably wider than 2 inches, and some decorative tumblers taper.
• Dishwasher: if the glasses are in daily rotation, reinforced crystal earns its keep. If they are hand-washed, it does not.

Rocks glass, lowball, old fashioned glass and tumbler all describe the same squat shape, and manufacturers use them interchangeably. Double old fashioned, DOF, double rocks and bucket glass all describe the larger version. There is no governing standard, which is why two glasses labelled rocks can differ by 5 oz.

The practical consequence: ignore the name on the listing and read the stated capacity in ounces. If a listing does not state a capacity, treat that as a reason not to buy it. Best rocks glasses is organised by capacity for exactly this reason.