You’ve bought a screen labeled 27 inches and need to convert to centimeters to know if it fits your desk. You hear a US weather forecast say 95°F and want to know roughly how many degrees Celsius — these “unit translations” happen every day. The metric-vs-imperial chaos isn’t your fault; it’s a historical legacy. This post helps you sort out the context and gives you the Piick unit converter to handle every scenario with one click.

Where the two systems came from

The metric system originated in France in the 1790s during the French Revolution. Scientists of the time decided to abandon all “the king’s foot” or “the king’s cubit” units based on human standards and instead use natural constants: one meter equals one ten-millionth of the meridian from the equator to the North Pole, and one gram equals the mass of one cubic centimeter of water. The logic is crystal clear: decimal, so any two units convert by a factor of 10.

The imperial system has over 1000 years of history, tracing back to ancient Roman and Anglo-Saxon measurements like “one foot = some king’s foot length” and “one pound = some farmer’s bag of wheat”. 12 inches = 1 foot, 3 feet = 1 yard, 1760 yards = 1 mile — chaotic bases, but because the British Empire colonized globally in the 18th-19th centuries, this system was forcibly brought to North America, India, and Australia.

The result: 95% of countries worldwide use metric, with only the US, Liberia, and Myanmar (informally) keeping imperial for daily use. But imperial has permeated the world through the English language and Anglo culture, so everyone has to learn a bit of it.

Which countries still use imperial

Looking only at “official measurement”, almost every country is metric. But “actual daily use” is more complex:

  • United States: Imperial for daily use (pounds, miles, Fahrenheit, gallons), but science, medicine, military, and exports must use metric. Car engines labeled 5.7L, but gas stations sell gallons
  • United Kingdom: Officially didn’t fully switch to metric until 1995, but miles, feet, and pounds remain common in daily life. Beer is sold by the pint, roads measured in miles
  • Canada: Dual system — officially metric, but imperial in everyday use. Weather in Celsius, height in feet/inches
  • Australia/New Zealand: Almost fully metric, but land area occasionally uses acres
  • Japan: Primarily metric, but room areas use “jo” (tatami mats), screen sizes use inches

So when you see “imperial vs metric” disputes, it’s fundamentally the tension between daily habits vs international standardization. The easiest traps to fall into are while traveling.

5 most-confused everyday units

These 5 are the ones I’m asked about most and the easiest to miscalculate:

  • Inches (in) vs centimeters (cm): 1 in = 2.54 cm (exact). Used for screens, tires, paper, umbrella diameter. A 15.6-inch laptop is about 39.6 cm diagonal
  • Fahrenheit (degF) vs Celsius (degC): It’s not a simple 2x relationship. The formula is F = C x 9/5 + 32. 30 degC = 86 degF, 100 degF = 37.8 degC. At -40, they’re equal (the only crossover point)
  • Pounds (lb) vs kilograms (kg): 1 lb = 0.4536 kg. The US uses pounds for body weight and food ingredients, China uses kilograms. A 5 lb bag of flour is about 2.27 kg
  • Ounces (oz) vs milliliters (ml): Both called “ounce” but in imperial, weight ounces (oz) are about 28.35 grams, while fluid ounces (fl oz) are about 29.57 ml. An 8 fl oz coffee is about 237 ml, not 227 grams!
  • Miles (mi) vs kilometers (km): 1 mi = 1.609 km. US highway speed limit 65 mph = 105 km/h

The easiest mistakes are with temperature and ounces (because of double meanings). Use a tool rather than mental math.

A small trick for one-click conversion

The Piick unit converter has hundreds of built-in units across 12 dimensions (length, mass, temperature, volume, area, speed, pressure, energy, power, time, storage, data). No signup, runs locally in the browser, no data uploaded.

Steps:

  1. Open the Piick unit converter; “Length” is the default tab
  2. Pick the source unit on the left (e.g., in), the target unit on the right (e.g., cm)
  3. Type the number on the left and the result appears instantly on the right. You can also reverse it
  4. Switch tabs to change dimension (temperature, mass, volume, etc.). The temperature tab shows side-by-side degF and degC
  5. (Optional) Click the “copy” icon next to the result to paste anywhere

Two small tricks:

  • Batch conversion: The tool supports pasting multiple values at once (one per line) and auto-outputs in bulk, great for making tables
  • Precision switching: The bottom-right lets you switch between 2 / 4 / 6 decimal places; use 6 for engineering calculations needing high precision

Next time you see “this oven is 350 degF”, “that distance is 5 miles”, or “this bag of sugar is 16 oz”, you don’t need to open a search engine anymore. Open the Piick unit converter and you’re done in a second, with higher precision than mental math.