English units

English units of measurement, like feet, miles, pounds, Fahrenheit and acres, are still common in the English-speaking world, particularly in America.

Everyone in the English-speaking world learns the metric system at school, since at least the 1980s, but many still think in English units, especially in everyday life. In America the metric system is mostly used for science, medicine, the Olympics, foreign car parts and large bottles of Coke.

There are two slightly different systems of English units:

• US customary system – set by American law
• Imperial system – used in the British Empire

The US customary system is still in heavy use. You see it on this blog sometimes. This post is mainly about that system. Differences with the Imperial system are noted at the end.

The English system grew out of the Roman one, in a time before anyone in England knew about zero. So it is not based on multiples of 10, like the metric system, but on 2, 3, 6, 12, 16 and so on, numbers that were easy to divide in your head.

The most commonly used units:

Length:

• 1 mile = 5280 feet = 1.609344 km (supposed to be a thousand paces or 2000 steps)
• 1 yard = 3 feet = 0.9144 m
• 1 foot = 12 inches = 0.3048 m (supposed to be the length of a man’s foot)
• 1 inch = 2.54 cm
• 1 nautical mile = 1.15078 miles = 1852.0 m (1 degree latitude = 60 nautical miles) m
• 1 rod = 5.0292 m

Mass (weight):

• 1 ton = 2000 pounds = 907.184 kg = 0.907184 metric tons
• 1 pound = 16 ounces = 453.592 g
• 1 ounce = 28.35 g
• 1 troy ounce (used for precious metals) = 8 drams = 31.103 g
• 1 dram  = 3 scruples =  3.889 grams
• 1 scruple = 20 grains = 1.296 grams
• 1 grain = 64.79891 mg

Volume:

• 1 barrel = 42 gallons = 158.97 L
• 1 gallon = 4 quarts = 3.785 L
• 1 quart = 2 pints = 0.94636 L
• 1 pint = 2 cups = 473.18 L
• 1 cup = 8 fluid ounces = 236.59 mL
• 1 fluid ounce = 2 tablespoons = 29.57 mL
• 1 tablespoon = 3 teaspoons = 14.79 mL
• 1 teaspoon = 8 dashes = 4.93 mL
• 1 dash = 0.62 mL
• 1 drop = 0.08 mL
• 1 bushel = 8 gallons = 30.28 L (a dry measure, like for wheat)
• 1 cubic foot = 28.32 L

Area:

• 1 square mile = 640 acres = 2.590 sq km
• 1 acre = 43,560 square feet = 0.4047 ha
• 1 square foot = 0.0929 sq m

Temperature:

• 212 Fahrenheit = 100 Celsius
• 68 Fahrenheit = 20 Celsius
• 32 Fahrenheit = 0 Celsius
• 0 Fahrenheit = -17.8 Celsius
• -40 Fahrenheit = -40 Celsius

Power:

• 1 horsepower = 0.745700 kW (mainly for engines)

Speed:

• 1 knot (for ships) = 1 nautical mile per hour = 1.852 kph
• 1 mph (mile per hour) = 1.609 kph

Time:

• Same as metric (seconds, minutes, hours, days, etc)

In America the average woman is 5 foot 6. That means 5 feet and 6 inches or 1.68 metres. It is sometimes written as 5’6″.

Strange abbreviations:

• lb = pound
• oz = ounce
• cwt = hundredweight (Imperial)

The Imperial system:

Some sizes were different. The biggest difference was in the gallon and the other units of volume: they were all 20% bigger. The ton, sometimes called a long ton, was 12% bigger (but the pound was pretty much the same):

• 1 yard = 0.914398416 m (not 0.9144 m)
• 1 gallon = 4.54609 L (not 3.785 L)
• 1 ton = 2240 pounds = 1016.047 kg (not 2000 pounds)

They also used:

• 1 league = 3 miles = 4.828 km (supposed to be an hour’s walk)
• 1 furlong = 660 feet = 201.168 m
• 1 fathom = 6 feet = 1.8288 m
• 1 hundredweight = 8 stone = 112 pounds = 50.8 kg
• 1 stone = 14 pounds = 6.35 kg

A nautical mile (1852 m) was just a bit over 1000 fathoms.

Roman units:

The Roman units that some of these go back to (American values in parentheses):

• 1 inch = 2.46 cm (2.54 cm)
• 1 foot = 0.296 m (0.3054 m)
• 1 mile = 1.48 km (1.609 km)
• 1 gallon = 4.33 L (3.785 L) – a dry volume
• 1 ounce = 27.3 g (28.35 g)
• 1 pound = 327 g (453 g)

– Abagond, 2011, 2021.

See also:

• metric system
• Attic units
• English
• England