Imperial vs U.S. Customary Units
British Imperial and U.S. customary measurement developed from older English units. They share many unit names, but they are distinct systems and should not be treated as interchangeable.
Why the Names Matter
The British Imperial System was established in the United Kingdom in the nineteenth century. The United States uses U.S. customary units. NIST recommends using the term "U.S. customary" for the U.S. system rather than calling it British or Imperial.
Shared Length Relationships
- 1 inch = exactly 25.4 mm
- 1 foot = 12 inches = exactly 0.3048 m
- 1 yard = 3 feet = exactly 0.9144 m
- 1 international mile = 1,760 yards = exactly 1.609344 km
Important Differences
Volume is the clearest everyday example: a U.S. liquid gallon is about 3.785 L, while an Imperial gallon is about 4.546 L. Their pints and fluid ounces therefore differ too. Some mass terminology also differs, including the U.S. short ton and British long ton.
Using the Online Ruler
The ruler supports centimetres, millimetres, and inches. Calibrate the current display before using its physical scale; the tool does not convert volume or mass units.