Speed unit conversion
Converts a speed value between meters per second, kilometers per hour, miles per hour, knots, and feet per second. Everything is converted through meters per second internally using standard definitions, so the figures line up with what you'd see on a car speedometer (km/h or mph), a ship or aircraft's instruments (knots), or a physics textbook (m/s).
Why meters per second is used as the internal reference unit
Meters per second is the SI base unit for speed, and every other unit here (km/h, mph, knots, ft/s) has an exact, internationally defined relationship to it - converting everything through one common reference unit keeps the math consistent and avoids compounding rounding error from converting directly between every possible pair of units.
Why knots specifically matter for marine and aviation contexts
A knot (one nautical mile per hour) is tied to the nautical mile, which is itself defined from a minute of latitude - a unit that maps naturally onto a ship or aircraft's position on a chart, which is why marine and aviation navigation standardized on it long before kilometers or miles were in common use for that purpose.
Why the mph-to-km/h relationship isn't a clean round number
A mile is defined as exactly 1,609.344 meters, a figure that has nothing to do with the metric system's own base-10 structure - so converting between a mile-based unit and a meter-based unit will never land on a perfectly round number, which is simply a consequence of the two systems having developed independently of each other.