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Converting km to miles uses a fixed conversion factor between kilometers (metric) and miles (imperial/US customary).
Key fact (exact relationship): \(1\ \text{mile} = 1.609344\ \text{km}\).
Equivalently, \(1\ \text{km} = \dfrac{1}{1.609344}\ \text{miles} \approx 0.621371\ \text{miles}\).
Step-by-step method (kilometers to miles)
- Start with the distance in kilometers, \(d_{\text{km}}\).
- Multiply by the km-to-miles factor \(0.621371\ \dfrac{\text{miles}}{\text{km}}\).
- Round to the precision needed for the context (navigation, running, engineering, etc.).
The conversion formula is:
\[ d_{\text{miles}} = d_{\text{km}} \times 0.621371 \]Worked example: convert 10 km to miles
Take \(d_{\text{km}} = 10\ \text{km}\). Multiply by the conversion factor:
\[ d_{\text{miles}} = 10 \times 0.621371 = 6.21371\ \text{miles} \]Rounded to two decimal places: \(6.21\ \text{miles}\).
Quick reference table
| Distance (km) | Distance (miles) | Rounded (2 d.p.) |
|---|---|---|
| 1 | \(1 \times 0.621371 = 0.621371\) | 0.62 |
| 5 | \(5 \times 0.621371 = 3.106855\) | 3.11 |
| 10 | \(10 \times 0.621371 = 6.21371\) | 6.21 |
| 42.195 (marathon) | \(42.195 \times 0.621371 \approx 26.2188\) | 26.22 |
| 100 | \(100 \times 0.621371 = 62.1371\) | 62.14 |
Visualization: proportional scaling from km to miles
Common checks and rounding guidance
- Sanity check: miles should be smaller than kilometers for the same distance because \(1\ \text{mile} > 1\ \text{km}\).
- Everyday rounding: two decimals is usually enough (e.g., 10 km → 6.21 mi).
- Fast mental estimate: use \(0.62\) as a quick factor, then refine with \(0.621371\) if needed.
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