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0.44704. Miles per hour ( mph, m.p.h., MPH, or mi/h) is a British imperial and United States customary unit of speed expressing the number of miles travelled in one hour. It is used in the United Kingdom, the United States, and a number of smaller countries, most of which are UK or US territories, or have close historical ties with the UK or US.
The kilometre, a unit of length, first appeared in English in 1810, [ 9] and the compound unit of speed "kilometers per hour" was in use in the US by 1866. [ 10] ". Kilometres per hour" did not begin to be abbreviated in print until many years later, with several different abbreviations existing near-contemporaneously. 1903: "KMph."
In the United States, speed limits are set by each state or territory. States have also allowed counties and municipalities to enact typically lower limits. Highway speed limits can range from an urban low of 25 mph (40 km/h) to a rural high of 85 mph (137 km/h). Speed limits are typically posted in increments of five miles per hour (8 km/h).
≈ 1 hour walk, Currently defined in US as 3 Statute miles, [3] but historically varied from 2 to 9 km ≈ 4828 m: light-day ≡ 24 light-hours ≡ 2.590 206 837 12 × 10 13 m: light-hour ≡ 60 light-minutes ≡ 1.079 252 8488 × 10 12 m: light-minute ≡ 60 light-seconds ≡ 1.798 754 748 × 10 10 m: light-second
25–35 miles per hour (40–56 km/h) (Varies by State) 55–85 miles per hour (89–137 km/h)[fn 19][fn 20] 40–65 miles per hour (64–105 km/h)[fn 21] Restrictions only in some states, typically 5–15 mph lower. None formally, though jurisdiction-dependent. Venezuela. 40–60 kilometres per hour (25–37 mph) 120[fn 22] 60–120.
The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour). [Note 3] According to the special theory of relativity, c is the upper limit for the speed at which ...
kilometre (km) or kilometer is a metric unit used, outside the US, to measure the length of a journey; the international statute mile (mi) is used in the US; 1 mi = 1.609344 km. nautical mile is rarely used to derive units of transportation quantity.
39–46 mph 62–74 km/h 17.2–20.7 m/s 18–25 ft 5.5–7.5 m Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind Twigs break off trees; generally impedes progress 9 Strong/severe gale 41–47 knots 47–54 mph 75–88 km/h 20.8–24.4 m/s