What is the difference between US units and Imperial units?

Answer 1

There are quite a few differences, mostly in that the US units are smaller than the imperial ones with the same names:

*With respect to lengths:

There doesn't seem to be much difference except that in America when specifying fairly long distances less than a mile they use feet instead of yards (which is slightly shorter than the metre).

* With respect to volumes:

1 US pt = 16 US fl oz

1 imp pt = 20 imp fl oz

→ 1 US gal = 128 US fl oz

→ 1 imp gal = 160 imp fl oz

But note that 1 US fl oz ≈ 1.041 imp fl oz so the US pint and gallon are slightly larger than 4/5 the imperial pint and gallon.

* With respect to mass:

Not so much the system but convention is that in America weights are expressed in pounds whereas the UK uses stones and pounds (where 1 st = 14 lb).

With the ton:

the US system uses the short ton of 2000 lb,

but the imperial system uses the long ton of 2240 lb.

This leads to 1 hundredweight (cwt) being difference as 1 ton = 20 cwt in both systems:

1 US cwt = 1 short cwt = 100 lb

1 imp cwt = 1 long cwt = 112 lb (= 8 st)

The US system also uses the slug where 1 slug ≈ 32.174 lb; it is the mass that accelerates at 1 ft/s² when a 1 pound force is applied to it.

A metric ton (1 tonne) is 1000 kg ≈ 2205 lb which is a close approximation to the imperial ton.