The Great Measurement Divide

  • Metric: Used by 95% of the world's population—base-10, logical, scientific standard
  • Imperial: USA, Liberia, Myanmar—feet, pounds, gallons (and $370M Mars probe crashes)
  • 1999 disaster: NASA's Mars Climate Orbiter burned up because one team used metric, another used imperial

Supported Categories

  • Weight/Mass (mg, g, kg, oz, lb, stone, ton)
  • Distance/Length (mm, cm, m, km, in, ft, yd, mi)
  • Area (mm², cm², m², km², in², ft², acre, hectare)
  • Volume (ml, l, m³, fl oz, cup, pint, quart, gallon)
  • Pressure (Pa, bar, atm, psi, torr, mmHg)
  • Temperature (°C, °F, K, °R)
  • Energy (J, cal, Wh, BTU, eV)
  • Power (W, kW, hp, BTU/h)
  • Speed (m/s, km/h, mph, knot, Mach)

Why These Weird Units Exist

  • Foot: Literally a king's foot length—Henry I of England standardized it around 1100 AD
  • Inch: Width of a man's thumb, or 3 barleycorns laid end-to-end (seriously)
  • Mile: Roman 'mille passus' = 1,000 double paces of a Roman legion soldier
  • Pound: From Latin 'libra pondo' (hence 'lb')—a pound weight of silver
  • Gallon: UK and US gallons differ! US: 3.79L, UK: 4.55L (20% more!)

Temperature: The Weirdest Scales

  • Fahrenheit (1724): 0° = coldest brine solution, 96° = human body temp (he was slightly off)
  • Celsius (1742): Originally inverted! 0° was boiling, 100° freezing—fixed by Linnaeus
  • Kelvin: 0K = absolute zero (-273.15°C)—atoms stop moving entirely
  • -40°: The only point where Fahrenheit and Celsius are equal!
  • Body temp: 98.6°F (37°C) was from 1851—modern average is actually 97.9°F

Quick Mental Conversions

  • km → miles: Multiply by 0.6 (or use Fibonacci: 5km ≈ 3mi, 8km ≈ 5mi)
  • kg → lbs: Double it and add 10% (70kg → 140 + 14 = 154 lbs)
  • °C → °F: Double and add 30 (rough), or ×1.8+32 (exact)
  • liters → gallons: Divide by 4 (roughly—actually 3.785)
  • meters → feet: Multiply by 3.3 (1m = 3.28ft)

Cooking Conversions (US)

  • 1 cup = 8 fl oz = 16 tablespoons = 48 teaspoons = 237ml
  • 1 tablespoon = 3 teaspoons = 15ml
  • 1 stick of butter = 8 tablespoons = 113g = 1/2 cup
  • 1 pound of flour ≈ 3.5 cups (varies by type!)
  • UK tablespoon = 15ml, Australian tablespoon = 20ml (watch recipes!)

Pressure: When Units Get Serious

  • 1 atm: Sea level air pressure = 101.325 kPa = 14.7 psi = 760 mmHg
  • Tire pressure: Car tires: 30-35 psi, bike tires: 80-130 psi
  • Scuba: Every 10m depth adds 1 atm—at 30m you're under 4 atmospheres!
  • Blood pressure: 120/80 mmHg—millimeters of mercury, a holdover from old instruments

Speed: Putting It in Perspective

  • Walking: 5 km/h (3.1 mph)—about 1.4 m/s
  • Usain Bolt: 44.72 km/h (27.8 mph) peak—faster than city speed limits!
  • Sound: 343 m/s (767 mph) at sea level, 20°C—Mach 1
  • Bullet: Handgun ~370 m/s, rifle ~1,200 m/s (Mach 3.5)
  • Light: 299,792,458 m/s—1 light-year = 9.46 trillion km

Energy: Calories vs Joules

  • 1 food Calorie (kcal) = 1,000 calories = 4,184 Joules
  • A Big Mac has 563 kcal = 2.36 million Joules (enough to power a 60W bulb for 11 hours)
  • 1 kWh = 3.6 million Joules (what your electricity meter measures)
  • Human body at rest burns ~80W continuously (like a light bulb!)
  • TNT equivalent: 1 ton TNT = 4.184 billion Joules (used for explosions & asteroids)

Area & Volume: Real-World Sizes

  • Football field: 1.32 acres = 0.53 hectares = 5,351 m²
  • Olympic pool: 2,500 m³ = 660,000 US gallons
  • Shipping container: 20ft standard = 33 m³, 40ft = 67 m³
  • Studio apartment: ~40 m² = 430 sq ft
  • Parking space: ~15 m² = 160 sq ft (varies by country)

Pro Tips

  • Always specify US vs UK gallons, cups, and tablespoons in recipes
  • Scientific work uses SI units exclusively—convert early, avoid errors
  • When buying internationally: check if 'oz' means fluid oz or weight oz
  • GPS uses meters internally—even in USA (it's a global system)
  • Drug dosages use metric worldwide—never approximate, always convert exactly