The English System of Units
The imperial units of length and mass, the factors joining inches, feet, yards and miles, ounces, pounds and tons, and how to convert between them.
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Most of the world measures in metres and kilograms. Some countries, the United States among them, still measure in inches, feet and pounds. This is the English system — and its conversion factors are nothing like the tidy powers of ten you are used to.
Concept
Two different systems
The metric system counts in centimetres, metres and kilometres. The English system uses an entirely separate set of names and sizes.
Metric: centimetre, metre, kilometre; gram, kilogram.
English: inch, foot, yard, mile; ounce, pound, ton.
They measure the same things — length and mass — but you cannot mix their units inside one calculation without converting first.
Concept
Units of length
A foot divides into 12 inches, a yard is 3 feet, and a mile is 5280 feet. The factors 12, 3 and 5280 have to be learnt — there is no pattern joining them.
Concept
Units of mass
Mass has its own set of English units, unrelated to grams:
1 pound = 16 ounces.
1 ton = 2000 pounds.
Ounces suit small weights, pounds suit people and groceries, and tons suit vehicles and cargo.
Example
Feet into inches
How many inches are there in 5 feet?
Each foot holds 12 inches.
⟹ 60 inches
Going from a larger unit to a smaller one, the count grows — so you multiply.
Example
Pounds into ounces
How many ounces are there in 3 pounds?
Each pound holds 16 ounces.
⟹ 48 ounces
The method never changes: identify the factor joining the two units, then multiply by it.
Note
Where each unit is used
Feet and inches — a person's height.
Yards — American football and other sports.
Miles — road distances and speed limits.
Pounds — body weight and shopping.
Tons — heavy loads and vehicles.
Summary
- The English system is separate from the metric system and still in use.
- Length: 1 foot = 12 inches, 1 yard = 3 feet, 1 mile = 5280 feet.
- Mass: 1 pound = 16 ounces, 1 ton = 2000 pounds.
- Convert from a larger unit to a smaller one by multiplying by the factor.
- The factors must be memorised — they follow no power-of-ten pattern.