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Alcohol Proof to ABV Converter

Everyday

Convert alcohol proof to ABV percentage and back, for both the US proof scale (2x ABV) and the old UK proof scale — for bartenders, distillers, and homebrewers.

Reviewed by the thecalcu.com team · Last updated July 10, 2026

From
To
All conversionsfor 1 US Proof
ABV (%)0.5
US Proof1
UK Proof (old system)0.87489064

What is a Proof/ABV?

An Alcohol Proof to ABV Converter translates between the "proof" labelling systems used on spirit bottles and the ABV (alcohol by volume) percentage that actually describes how much of the liquid is pure alcohol. Two different proof systems exist historically, the US system, where proof is always exactly double the ABV percentage, and the older UK system, based on a different historical reference point that corresponds to roughly 57.15% ABV at 100° proof.

Because both systems use the same word "proof" but mean different things numerically, converting correctly requires knowing which system applies to your bottle or recipe. This tool keeps US Proof and UK Proof as separate selectable units specifically to avoid that common mix-up.

Why Use an Alcohol Proof to ABV Converter?

Spirit bottles, cocktail recipes, and historical distilling references often label alcohol content in proof rather than percentage, but nutritional information, standard drink calculations, and most modern recipes use ABV percentage instead. Converting incorrectly, especially confusing US and UK proof, can lead to a significant misunderstanding of a drink's actual alcohol strength.

Two concrete situations this solves: converting a US-labelled "100 proof" bourbon bottle into its 50% ABV equivalent to compare against a wine or beer's percentage, and converting a vintage UK spirit's "70° proof" label (using the old UK system) into its correct modern ABV percentage rather than mistakenly applying the US doubling formula.

Who Should Use This Converter?

  • Bartenders and mixologists converting between proof and ABV when following recipes or spec sheets that mix labelling conventions.
  • Homebrewers and distillers (where legally permitted) converting calculated or measured ABV into standard proof for labelling and record-keeping.
  • Spirits collectors and enthusiasts interpreting vintage bottle labels that use the historical UK proof system.
  • Hospitality and bar management students learning the standard conversion between US proof and ABV percentage.
  • International spirits importers cross-referencing US proof labelling against the ABV percentage convention used in India and most of the world.

What Insights Does the Proof/ABV Converter Give You?

Converting to ABV (%) gives you the universally understood alcohol content figure used on most international labels, nutritional calculators, and standard drink measurements. Converting to US Proof or UK Proof gives you the region-specific proof rating, useful when labelling a spirit for a market that expects proof notation or interpreting an existing proof-labelled bottle correctly.

Because US and UK proof use different reference points for the same term, the two conversion factors in this tool (÷2 for US, ÷0.5715 for UK) produce meaningfully different ABV results from the same proof number, always double-check which system applies to your specific bottle or context before relying on the converted value.

How to use this Proof/ABV calculator

  1. Select your starting unit from the From dropdown, ABV (%), US Proof, or UK Proof (old system).
  2. Enter your value, such as 80 for 80 proof.
  3. Select your target unit from the To dropdown, such as ABV (%).
  4. Read the converted result, which updates instantly.
  5. Use the swap (⇅) button to convert an ABV percentage back into proof for either system.
  6. Double-check whether your source bottle or recipe uses the US or UK proof convention before applying the result, since the two systems are not interchangeable.

Formula & Methodology

All units convert through ABV percentage as the base unit, using the fixed relationships defined by each proof system:

US: ABV (%) = US Proof ÷ 2  |  US Proof = ABV (%) × 2
UK (old system): ABV (%) = UK Proof × 0.5715  |  UK Proof = ABV (%) ÷ 0.5715

Worked example: Converting 90 US proof to ABV, 90 ÷ 2 = 45% ABV. Converting that same 45% ABV to the old UK proof scale instead: 45 ÷ 0.5715 ≈ 78.7° UK proof, illustrating why the same spirit yields a different-looking proof number under each historical system.

Frequently Asked Questions

ABV (%) = US Proof ÷ 2, since US proof is defined by law as exactly twice the alcohol-by-volume percentage. For example, 80 proof bourbon converts to 80 ÷ 2 = 40% ABV.
In the US system, 100 proof means the spirit is 50% alcohol by volume, the proof number is always exactly double the ABV percentage, a convention set by US federal alcohol regulations (TTB). This converter applies that exact 2:1 relationship.
The old UK (British) proof system used a different reference point, 100° UK proof corresponds to approximately 57.15% ABV, not 50% like the US system, based on a historical gunpowder test rather than a direct doubling of ABV. The UK officially replaced this system with ABV labelling in 1980, but the old proof scale still appears on some vintage spirits and in historical contexts.
Select ABV (%) as your From unit, enter the percentage (such as 40), and select US Proof as your To unit, the tool multiplies by 2 automatically, giving 80 proof. This is the reverse of the standard proof-to-ABV calculation.
Proof is a historical labelling convention that predates modern ABV percentage labelling, the term originates from 18th-century British sailors who 'proved' a spirit's alcohol content by checking whether gunpowder soaked in it would still ignite. Many countries, including the US, still print proof on spirit labels alongside or instead of ABV percentage as a matter of tradition and regulation.
Most whiskey and vodka are bottled around 80 US proof (40% ABV), though cask-strength and overproof spirits can reach 120-140+ proof (60-70%+ ABV). Beer typically ranges from 3-6% ABV, and wine from about 11-15% ABV, well below the range where proof labelling is commonly used.
Select ABV (%) as your From unit, enter your measured or calculated ABV, and select US Proof as your To unit to get the proof value for labelling purposes. Always check local regulations, as homemade distillation is restricted or illegal in many jurisdictions without a licence, including in most of India.
Yes, overproof rum typically refers to bottlings above 100 US proof (50% ABV), often reaching 151 proof (75.5% ABV) or higher, compared to standard rum's usual 80 proof (40% ABV). This converter can quickly translate an overproof rum's proof rating into its actual ABV percentage for safe consumption awareness.
India uses ABV percentage as the standard labelling convention for alcoholic beverages, following international norms, rather than the proof system historically used in the US and UK. This converter is most useful in India when working with imported spirits or historical/US-sourced recipes and labels that reference proof instead of percentage.
The two systems use different reference points for the same word 'proof', a bottle labelled '100 proof' means 50% ABV under the US system but approximately 57.15% ABV under the old UK system, so using the wrong conversion would give a significantly incorrect ABV. This converter keeps the two systems as separate selectable units to avoid that common source of error.
Also known as
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