The three "tons" — always specify which one
The word "ton" refers to three different units depending on context: US short ton (2,000 lb / 907 kg), UK long ton (2,240 lb / 1,016 kg), and metric tonne (1,000 kg / 2,205 lb). In international trade and shipping, always clarify which ton you mean. The converter labels all three clearly to avoid ambiguity.
Celsius to Fahrenheit — the quick mental math trick
For approximate conversion without a calculator: double the Celsius temperature and add 30. This gives a result within 5°F for temperatures between 0°C and 40°C. For example: 20°C → (20×2)+30 = 70°F (actual: 68°F). Not precise enough for science, but fine for deciding what to wear.
Speed limits abroad — what to expect
European motorway speed limits are typically 120–130 km/h, which is 75–81 mph. A UK motorway at 70 mph is 113 km/h. If you are driving in a country that uses the opposite system to what you are used to, set the converter on your phone before you leave and note the key limits (30 km/h urban zones = 18.6 mph, 50 km/h = 31 mph, 100 km/h = 62 mph).
Data transfer rates — bits vs bytes
Internet service providers advertise speeds in megabits per second (Mbps). File sizes are shown in megabytes (MB). To find your actual download speed in MB/s, divide Mbps by 8. A 100 Mbps connection downloads files at approximately 12.5 MB/s. This is a source of enormous confusion and occasional consumer complaints — "my 100 Mbps internet only downloads at 12 MB/s!"
Area conversions for real estate
Property sizes are quoted in square feet (US), square metres (most of Europe), or occasionally acres/hectares for land. Key conversions: 1 square metre = 10.764 square feet. 1 acre = 4,047 square metres = 43,560 square feet. 1 hectare = 10,000 square metres = 2.471 acres. For mental reference: a standard American football field is about 0.5 hectares (5,000 square metres).