Speed Converter

From road signs to rocket science

Speed units multiply the confusion of length units because they combine a distance unit with a time unit, and different countries — and different fields — settle on different pairings. Road signs in the US show miles per hour while most of the rest of the world uses kilometres per hour. Sailors and pilots measure speed in knots. Scientists and engineers default to metres per second, the SI-consistent unit. This tool covers all of them, plus Mach, the ratio used for aircraft speed relative to the speed of sound.

How each unit is defined

A knot is one nautical mile per hour, equal to about 0.514 m/s — slightly faster than one mile per hour on land because a nautical mile (1,852 m) is longer than a statute mile (1,609.344 m). Feet per second is common in ballistics, engineering, and some sports contexts (like measuring a pitch or a swing). Mach number isn't a fixed unit like the others — it's the ratio of an object's speed to the local speed of sound, which itself varies with altitude and air temperature. This tool uses a standard sea-level approximation of 343 m/s for the speed of sound, which is accurate for general reference but should not be used for precise aerospace engineering, where the actual local speed of sound must be calculated from real atmospheric conditions.

Everyday and specialist applications

Travellers renting a car abroad convert unfamiliar speed limits into units they instinctively understand. Runners and cyclists convert pace and speed data between metric and imperial fitness apps. Sailors and pilots move between knots and other units when cross-referencing charts, weather reports, and equipment manuals that don't always share the same convention. Students and hobbyists exploring basic aerodynamics use the Mach conversion to get an intuitive feel for how fast supersonic and hypersonic speeds actually are compared to a car or a commercial jet.

A note on accuracy

Because m/s is used as this tool's internal base unit, every conversion first multiplies your input by the "from" unit's m/s-equivalent, then divides by the "to" unit's m/s-equivalent — the same two-step method used throughout this site. This keeps results consistent no matter which pair of units you choose, and avoids compounding rounding errors that can occur when chaining together dozens of separate conversion charts.

Quick reference

100 km/h is about 62.1 mph or 27.8 m/s. A brisk walking pace is roughly 1.4 m/s (5 km/h). Commercial jets cruise around Mach 0.85, or roughly 900 km/h at altitude. The reference table below the calculator lets you see how your chosen speed compares across every unit on this page in one glance.

A note on rounding

Speed conversions compound quickly over long distances or durations, so for navigation, sports timing, or engineering contexts, keep as much decimal precision as the source data supports rather than rounding early, especially when a small speed error could translate into a meaningfully large position or timing error downstream.

Comparing fitness data across apps

Many fitness trackers let you switch between metric and imperial display, but exported data files don't always update consistently, so if you're combining data from two different apps or devices, running a quick manual check with this converter is a reliable way to confirm both data sets are actually speaking the same unit before you compare pace or speed trends over time.