# R5 | anthropic/claude-opus-5 | run 2

## Prompt

How many kilometers are in 100 miles? Show the conversion factor and cite a source for it.

## Response

100 miles = 160.9344 kilometers.

## Conversion Factor

The exact, internationally agreed factor is:

\[ 1 \text{ mile} = 1.609344 \text{ km} \]

This follows from the 1959 International Yard and Pound Agreement, which defined 1 international yard as exactly 0.9144 meters. Since 1 mile = 1,760 yards:

\[ 1760 \times 0.9144 = 1609.344 \text{ m} = 1.609344 \text{ km} \]

## Calculation

\[ 100 \times 1.609344 = 160.9344 \text{ km} \]

Rounded for practical use: **160.9 km** (or roughly 161 km).

## Source

The definition is documented by the U.S. National Institute of Standards and Technology in its guide to SI units and conversion factors: [NIST Special Publication 811](https://www.nist.gov/pml/special-publication-811). The underlying yard definition appears in the 1959 Federal Register notice on refinement of values for the yard and pound, also archived by [NIST](https://www.nist.gov/pml/us-surveyfoot/revised-unit-conversion-factors).

Would you like the reverse conversion (kilometers to miles) or a quick reference table for common distances?
