UK Proof whisky vs. US Proof whiskey: the Difference Explained

Sunday, 26 October 2025 at 12:10

Sometimes you’ll come across a whisky that lists its strength in proof instead of ABV. Proof is another way of expressing alcohol content, but the system in the United States differs from the one historically used in the United Kingdom. Here’s how they compare.

FAQ

What is proof?
A measure a beverage's alcohol content.
Where did proof originate from?
From the British Royal Navy.
How many versions of proof are there?
Two.

UK Proof vs US Proof at a glance

UK Proof

Originated in the 16th century as a taxation measure.
Since 1816, defined as roughly 1.75 times the alcohol by volume.

US Proof

Adopted from Great Britain in 1848.
Defined as alcohol by volume multiplied by two.

What is the UK version of Proof?

In the United Kingdom, alcohol has been taxed since the 16th century. Distillers paid tax based on the strength of their spirit.

England distinguished between over proof and under proof using the burn-or-no-burn test: they checked whether the spirit would ignite. If the distiller’s liquid sustained a flame, it was classed as over proof. If not, it was under proof.

Another way to determine whether a spirit was proof was the gunpowder test. It was just as straightforward: gunpowder was soaked with the spirit and then lit. If it continued to burn, the spirit was over proof. If it didn’t, it was under proof.

In 1816, the Proof Act formalized the scale, setting Proof at approximately 1.75 times the alcohol by volume.

Today, the United Kingdom uses alcohol by volume (ABV). Still, there’s one whisky traditionally bottled at a Proof strength: Glenfarclas 105.

What is the US version of Proof?

In the United States, proof came later. The term appeared in 1848, influenced by British colonial America. By then, gunpowder tests and similar methods had already fallen out of use in the UK.

Instead, Americans adopted a simple calculation for whiskey and other spirits: each percent of alcohol equals two proof. So a bottle at 50 percent alcohol is 100 proof.

This system is still used in the United States today. You’ll find the proof statement on every bottle of bourbon or American whiskey.

Modern regulations also require bourbon and American whiskey labels to show the alcohol by volume. This can be listed alongside the proof.

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