What are Cask Strength, Barrel Proof, Overproof & Navy Strength?

Many different terms are used on labels to indicate the alcohol by volume (ABV) of the spirits inside. These can be fanciful and descriptive words, phrases, or terms recognized by the Alcohol and Tobacco Tax and Trade Bureau (TTB). Sometimes it is easiest to just look at the number in small font size at the bottom to know the truth.

Frey Ranch Farm Strength Uncut Bourbon, for example, is bottled at 60% to 66% ABV, depending on the batch. They explain that “farm strength” is “inspired by how we like to enjoy our whiskey on the ranch.”

Cask Strength, Barrel Proof, and Batch Strength

The description on Frey Ranch’s website is, “Every time we blend a small batch of our flagship four-grain bourbon, we taste it at cask strength before we ‘proof it down’ to our signature 90 proof [for the signature Straight Bourbon Whiskey]. We always fall in love with the uncut flavor, now you can too.”

The label also describes the bottling as cask-strength. Cask strength is a recognized term, even if it doesn’t correspond to a specific proof. According to Title 27 of the US Code of Federal Regulations:

The term “barrel proof” or “cask strength” may be used to refer to distilled spirits stored in wood barrels only when the bottling proof is not more than two degrees lower than the proof of the spirits when the spirits are dumped from the barrels.

Depending on what proof the spirit entered the barrel, and how long and where it aged, the bottling strength of a spirit sold in the US can be as low as 40% ABV (that can be found in long-aged scotch whisky) and up to much higher proof in American whiskey – as we’ll see in a few paragraphs.

Tamdhu Speyside Single Malt Whisky offers a cask-strength whisky blend, but they use the term “batch strength” for it. A representative from defined it as, “Batch Strength differs from Cask Strength as the final blend of whisky is from several casks without dilution.”

Full Proof or Original Proof

Some producers add water to ensure the final proof of a spirit in the bottle is the same as the proof of the spirit when it entered the barrel. The TTB also recognizes this under a few names.

The term “original proof,” “original barrel proof,” “original cask strength,” or “entry proof” may be used only if the distilled spirits were stored in wooden barrels and the proof of the spirits entered into the barrel and the proof of the bottled spirits are the same.

This term is usually used in American whiskey, where the spirit gains proof while aging, unlike in Scotland where spirits lose alcohol over time in the barrel. While this isn’t a super common term used on bottle labels, an example is 1792 Full Proof Bourbon “Bottled at its original 125 barrel entry proof, just as it was years ago when the barrels were first filled.”

High Proof, Hazmat, and Other Relative Proofs

“High proof” generally indicates that the proof of a product is higher than normal. Examples include Breckenridge Distillers High Proof bourbon and G4 Tequila Blanco High Proof 108.

Argonaut California Brandy offers a “saloon strength” bottling at 91 proof, “developed by bartenders for bartenders” to mix into cocktails and originally only available to on-premise accounts, though it’s now available at retail. Their other bottlings come in at around 43% ABV, which is still higher than most aged grape brandies like cognac.

In the past few years, whiskies have been reaching higher and higher bottling strengths, inspiring some people to call them “hazmat” whiskies, referring to “hazardous material.” The term could be seen as derogatory, but more often it seems to be used as a macho superlative.

The unofficial term indicates that the spirits were bottled at above 70% ABV (140 proof), and examples include Jack Daniels' Coy Hill High Proof, and Wyatt Earp "Hazmat" 13yr whiskey that actually put the word on the label.

Bottled In Bond

Another officially recognized proof is found on all bottled in bond spirits sold in the United States. The term (or synonyms “bond,” “bonded,” or “aged in bond” ) refers not to just the required bottle strength of 50% ABV, but to a minimum aging period of four years and other production factors.

While the term is mostly used for American-made bourbon, it can be applied to other aged spirits like rum or brandy, as well as spirits from other countries that meet the criteria. An example would be Brother’s Bond Bottled-In-Bond Straight Bourbon Whiskey.

Still Strength and Distilled to Proof

The term “still strength” indicates that the spirit goes into the bottle without dilution (or aging) after distillation. Like cask strength, this term doesn’t indicate any specific ABV. Many spirits are traditionally distilled to proof, including traditional mezcal and Peruvian pisco. In recent years, some tequila brands including El Tequileno have been advertising still strength bottlings a bit higher proof than the standard 40% ABV.

Vodka is not bottled at still strength (though legally I believe it could be), as it must be distilled to 95% ABV. It is known as ‘neutral spirits’ at that strength. Most gin also begins as a neutral spirit that is redistilled with botanicals including juniper. In this redistillation step, the neutral spirit is usually watered down, causing at least one brand to label its gin accordingly: The Botanist Distiller’s Strength. It is bottled at 50% ABV, not radically higher than their standard bottling at 46%.

Overproof and Navy Strength

The terms “overproof” and “navy strength” are used in different ways by different brands, based largely on a (mis)understanding of how the British navy measured proof in the early 1800s. These terms are often applied to gin and rum specifically, as these were both carried as rations on ships. Some people refer to “overproof” as more than 50% ABV, though this seems to be used less in gin and rum than other spirits.
Many gin brands use 57% ABV as their minimum for navy strength, including Edinburgh Gin, Four Pillars, Conniption, Hayman’s, and Plymouth.

For navy rum, brands usually choose either 54.5% ABV (including Mainbrace Navy Strength, while Pusser’s calls this ABV ‘Gunpowder Proof’) or else 57% ABV. Mount Gay Rum offers an Eclipse Navy Strength bottling at 57.1% ABV and Hamilton Navy Strength is 57%.

But Matt Pietrek of RumWonk.com has spent a good amount of time researching and writing about traditional British proof and rums. To summarize one of many posts on the historical accuracy of the terms, “navy strength” should be 54.5% ABV, “proof strength” is 57% ABV, and “overproof” should be anything above proof strength. It seems that less brands use the historically accurate proofs than the generally accepted ones.

So, despite the many different terms used to describe the strength of spirits, almost none of them point to specific ABVs. Most will merely get you in the ballpark.