Meter per Hour to Mile per Second

Most valley glaciers advance at 20–200 m/h (0.5–5 m/day). Surge glaciers — which periodically accelerate — can reach 1,000–10,000 m/h for months at a time. The Jakobshavn Glacier in Greenland holds the record for the fastest sustained glacier flow at roughly 4,600 m/h (46 m/day). For context, that's still far slower than a garden snail.

Human scalp hair grows at roughly 15 cm per year — about 0.017 mm/hour, or 0.000017 m/h. Nails grow at about half that rate. At this scale, even the m/h unit is too large; growth biologists use mm/day or cm/month. The fastest-growing human tissue is bone marrow, not hair.

Some lava flows on gently sloping terrain advance at about 1 m/h. Tectonic plates move at 2.5–15 cm/year — far below even 1 m/h. Bread rising in a warm kitchen expands at a few mm/hour. Corrosion front advancement in protected steel structures can be tracked in mm or cm per year.

m/h and m/hr are both used for meters per hour — neither is an official SI notation, since the SI symbol for hour is h (not hr). The correct SI notation is m/h. In engineering documentation, m/hr appears frequently as a stylistic choice, particularly in American engineering texts that prefer "hr" over "h" for legibility.

Multiply by 24,000. One m/h = 1,000 mm/h × 24 h/day = 24,000 mm/day. This conversion is useful in hydrology (soil permeability is measured in mm/day) and biology (plant growth, wound healing rates). A glacier moving at 100 m/h would be advancing 2,400,000 mm/day — or 2.4 km/day, which is an exceptionally fast surge.

The speed of light in a vacuum is exactly 299,792,458 m/s, which converts to approximately 186,282.397 mi/s. Before the SI system was globalised, US and British scientific texts routinely used this figure. The value 186,000 mi/s appears as a rounded approximation in older textbooks. Today, physicists universally use c = 3 × 10⁸ m/s or the exact SI value.

The solar wind — a stream of charged particles ejected from the Sun's corona — travels at roughly 250–500 mi/s (400–800 km/s) depending on whether it is the slow or fast component. During coronal mass ejections, bursts can exceed 1,200 mi/s (2,000 km/s). At 500 mi/s the solar wind crosses the 93-million-mile Earth–Sun gap in about 2 days, which is why space weather forecasters can give roughly 48 hours' notice before a geomagnetic storm hits.

Yes — several. NASA's Parker Solar Probe reached about 430,000 mph (119 mi/s or 192 km/s) at perihelion, making it the fastest human-made object ever. High-powered railgun projectiles tested by the US Navy reached around 2.5 km/s (1.5 mi/s). Intercontinental ballistic missiles (ICBMs) reach approximately 4 mi/s during their boost phase.

Exactly one second — that's the definition. At 1 mi/s you would cross the Atlantic Ocean (about 3,400 miles) in under an hour, reach the Moon (238,855 miles) in about 2.8 days, and reach the Sun (93 million miles) in roughly 12 days. The speed is conceptually useful for calibrating astronomical distances in imperial terms.

Rarely. The main residual use is in some US military ballistics documents and historical astrophysics references. The International Astronomical Union and NASA primarily use km/s for planetary and solar system speeds, and AU/year or c (fraction of light speed) for interstellar scales. Mi/s survives mostly in popular science writing aimed at American audiences unfamiliar with metric.