Metrified English Unit

Nowadays all Imperial Unit s are defined in terms of their Metric / SI equivalents, but mostly with quite odd factors. This choice was made to ensure largest possible continuity, but over time there have been several proposals to round off the values, which is thought to ease transition towards the metric system.

ROYAL SYSTEM

One of the earliest still known and most extensive proposals of a metrified Imperial system is from the early 1820s and is attributed to William Huskisson , but it wasn't embodied into the 1824 reformation of the Imperial system at all.

Length

There is also a version with a ''nautical mile'' of 1.85 km, which is much closer to 1' of the circumference of Earth and its current value of 1.852 km. The mile is about ¼ Mrad Earth, while a kilometre was at that time believed to be 0.01 Grad Earth.
The pace was originally 2½ foot, i.e. 30 inches or 7.5 dm, but with 32 inches or 8 dm a mile retains both its definitions: the old Roman one of being 1000 ''gradus'' and the English one of 8 ''furrows long''. Also note, that a 1.8-km seamile is 2 000 yards or nine furlongs.

Area

For area measurement of course all length units can simply be squared, e.g. 1 foot&² = 9 dm&². Those are not explicitly listed here.

Volume, capacity

For volume measures of course all length units can simply be cubed, e.g. 1 foot³ = 27 dm³ = 27 l. Those are not explicitly listed here.
There are at least two gallon-based variants, one with a 4-litre gallon, the other with a 5-litre one. With 5 litre a gallon of water still weighs 10 pounds; note the correspondence between the volume and mass units which share a name.

Mass, weight

The Troy Pound gets replaced by the ''libra'', the abbreviation for the real pound has to change accordingly.

Derived units

The ''knot'' is acknowledged as 1 nautical mile per hour.

Weight and mass are often confused and it is not surprising, that in many proposals there is no explict mention of (gravitational) force, but the Pound-force is still 1 pound times Gee , see also Kilopond .
The Poundal (1 lb.·ft./s&²) equals 0.15 N with the above redefinitions of pound and foot.

Likewise you get the units of ''pressure'', e.g. Pound-force/inch&² or ''inch mercury''. For ''energy'' or heat, a British Thermal Unit is almost exactly 1 KJ already. The units of power are rather new, but it makes sense to round a Horse Power to 750 W .

Kitchen

There are other metrified values for ''cup'' (240 mL or 250 mL), ''tablespoon'' (15 mL or 20 mL) and ''teaspoon'' (5 mL) in use today, independently from all the other units.

AMERICAN INDEPENDENCE

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At the First Congress , which met in 1789 when the metric system had not yet been developed in France, the system of units to be used in the future USA was one point of discussion. The Congress would have had (and still has) the constitutional right (article I, section 8) to decide on a standard of weights and measurement, but ''never'' did so.

In the meeting Thomas Jefferson was employed to find the best system of weights and measures to be used in the USA. The decimal Dollar had already been introduced at that time. In mid-1790 he proposed two systems of units, one evolutionary with a mere refinement of definitions and simplification of the existing English system, the other one revolutionary being decimal and only reusing some of the traditional names.

In coordination with scientists in France, he selected the Second Pendulum at 45° latitude as the basic reference. The pendulum was estimated to be 39.14912 English inches of that time long (an inch was much later defined to be 25.4 mm), that is about 994,4 mm, or 1.5 times that for a vibrating rod (58.72368 inches).

In the evolutionary approach, the foot was to be derived from one of these lengths by a simple integer factor, which would be either three (pendulum) or five (rod), i.e. lengthening it from the traditional value by 1.04970¯6 inches to ca. 331.463 mm or shortening it by 0.255264 inches to ca. 298.317 mm. For practical purposes he wanted the rod to be 58¾ (new) inches long, an increase of less than 0.045%.

The revolutionary system was quite similar to the metric system, except the mentioned difference of about 5½ mm between the second pendulum at 45° and the 10,000th part of the distance from the northpole to the equator, which became the first definition of the metre. Also it didn't have the concept of prefixes at all. A very similar system was a base of discussion in France after the revolution of 14 July 1789 , with Jefferson observing.

ISOLATED

Besides redefinitions of the whole system, which try to keep the values close and the system immanent factors intact, there were and are Simple Approximations of Imperial units in metric.

Length

; point (352 7/9 µm) : 250 µm = ¼ mm, 350 µm, 375 µm = 3/8 mm
; inch (25.4 mm) : 2.5 cm = ¼ dm, 3 cm
; foot (12 inch = 0.3048 m) : 2.5 dm = ¼ m, 3 dm, 3.¯3 dm = 1/3 m
; yard (3 foot = 0.9144 m) : 0.9 m, 1 m
; fathom (6 foot = 1.8288 m) : 1.8 m, 1.85 m, 1.852 m, 2 m
; rod, pole, perch (192 inch = 5.0292 m) : 5 m
; chain (4 rod = 20.1168 m) : 20 m
; cable (1/10 sea mile) : 180 m, 185 m, 185.2 m, 200 m
; furlong (10 chain = 201.168 m) : 200 m
; mile (8 furlong = 1.609344 km) : 1.5 km, 1.6 km, 1.609 km, 1.61 km, 2 km
; nautical mile (6080 foot = 1.853184 km) : 1.8 km, 1.85 km, 1.852 km, 1.853 km, 1.9 km, 2 km; 1 equatorial minute, 1 meridian minute

Area

; acre (4046.8564224 m&²) : 40 a, 40.5 a, 50 a = ½ ha

Volume, capacity

; scruple (1/3 drachm ≅ 1.184 ml) : 1 ml, 1.2 ml, 1.25 ml = 1¼ ml

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Metrified English Unit