How is US Proof to ABV Percent calculated?

Both scales are normalized through ABV percent, then converted using a fixed ratio.

Is the mirror direction available?

Yes. Use the switch button or open the ABV Percent to US Proof page.

Can I use decimal inputs?

Yes. Decimal strength values are supported for lab, labeling, and mixology use cases.

proof (US) to % ABV

1 US Proof = 0.5 ABV Percent · fixed factor via canonical reference constants · no offset

Direct Answer

1 US Proof equals 0.5 ABV Percent

This conversion uses a fixed factor based on canonical reference constants.

For 0.25 US Proof, the result equals 0.125 ABV Percent.

Converter Calculator

US Proof (proof (US))

1 US Proof (proof (US)) =
0.5 ABV Percent (% ABV)

Explanation

Multiply by 0.5 because 1 proof (US) corresponds to 0.5% ABV and 1 % ABV corresponds to 1% ABV. US proof is defined as 2 times ABV.

US Proof to ABV Percent follows one canonical fixed-factor definition tied to canonical reference constants, keeping calculator output and table values aligned.

Manual spot checks match the displayed values because calculator and table share the same conversion definitions.

Method & Reference (Verified)

Method basis: US Proof to ABV Percent uses the page-specific conversion model shown in Direct Answer.
Applied factor: 1 US Proof = 0.5 ABV Percent (as defined for this route).
Consistency rule: calculator output and table values use the same constants and rounding policy.

Common Conversion Values

US Proof (proof (US))	ABV Percent (% ABV)
0.25	0.125
0.5	0.25
1	0.5
5	2.5
12	6
20	10
40	20
57.15	28.575
80	40
100	50