Mile per Hour to Foot per Hour

The UK officially began metrication in 1965, but road signage was exempted to avoid the enormous cost of replacing signs. The 1969 decision to postpone road metric conversion was intended as temporary, but no subsequent government has prioritized the change. A 2021 review considered reverting the post-Brexit UK to imperial in other areas too, but road signs remain mph by law (The Traffic Signs Regulations and General Directions).

The Saffir-Simpson Scale defines a hurricane as sustained winds of 74 mph or more. Category 5 begins at 157 mph. The strongest recorded tropical cyclone was Typhoon Tip (1979) with 190 mph sustained winds. For context, a Category 1 hurricane at 74 mph will rip roof shingles and topple shallow-rooted trees; Category 5 causes catastrophic structural damage.

Aroldis Chapman set the official MLB record with a pitch recorded at 105.1 mph in 2010. The ball travels the 60.5 ft (18.4 m) from mound to plate in about 0.39 seconds — leaving the batter about 0.15 seconds to react after recognising the pitch type. For comparison, a tennis serve record is 163.7 mph (Sam Groth, 2012).

60 mph is 96.56 km/h — close but not the same. The actual crossover is at 62.137 mph = 100 km/h. Many countries set urban motorway limits at 100 km/h partly because it approximates a round 60 mph for visitors from mph-using countries. The error is about 3.5%, negligible for driving but meaningful for engineering calculations.

The 55 mph national speed limit was set in 1974 during the oil crisis — Congress chose it to maximize fuel economy, not because it was a round number. When the federal mandate was lifted in 1995, states picked 65, 70, or 75 mph based on traffic engineering studies of the 85th-percentile speed drivers naturally travel on a given road. Texas has the highest posted limit at 85 mph on a toll road near Austin. The seemingly arbitrary numbers are actually data-driven safety thresholds, not aesthetic choices.

Tectonic plates move at 2–15 cm/year on average — far below even 1 ft/h. However, during episodic "slow-slip events" on faults (a kind of slow-motion earthquake), the fault face can creep at detectable rates closer to mm/day. True ft/h movement would be catastrophic — the San Andreas Fault creeping at 1 ft/h would translate to 2.4 miles/day, far exceeding any measured geological rate.

Metal extrusion (forming rods or tubes by forcing material through a die) often runs at 1–100 ft/h depending on the alloy and die profile. Some ceramic and glass fiber drawing processes operate in this range. Paper mill wet-end press sections can be as slow as 10–50 ft/h during startup. These speeds are slow enough that workers can safely observe and adjust the process manually.

Icebergs drift with ocean currents at roughly 0.5–1 km/day, equivalent to about 55–110 ft/h. Calving glaciers can lurch forward at thousands of ft/h during surge events. The famous 2017 calving of iceberg A-68 from the Larsen C ice shelf happened over a period of days — so its "speed" of separation was only a few ft/h at most.

It depends on the magnitude. 1 ft/h = 24 ft/day = 288 in/day — for something moving a few feet per hour, inches per day becomes a large awkward number. Conversely, for very slow movement (0.01 ft/h = 2.88 in/day), in/day gives a cleaner number. Engineers choose whichever unit gives a value between roughly 1 and 1,000 to minimize leading zeros.

Sea stars (starfish) move at roughly 0.06 m/min, which is about 11.8 ft/h — surprisingly fast. Coral polyps and sea anemones are essentially sessile but can contract at a few mm/min. Some fungi extend their hyphal tips at 1–4 mm/h — about 0.003–0.013 ft/h. Slime molds (Physarum polycephalum), often used in computing research, can advance at up to 4 cm/h (about 1.3 ft/h).