Unit Converter

Multiply miles by 1.609344 to get kilometers. The exact definition: 1 mile = 1,609.344 meters (NIST SP 811, derived from the 1959 International Yard and Pound Agreement where 1 yard = 0.9144 meters exactly, and 1 mile = 1,760 yards). Examples: 5 miles = 8.05 km (a common running race distance), 26.2 miles = 42.195 km (marathon), 60 mph = 96.56 km/h. Quick mental math: multiply by 1.6, or add 60% (10 miles + 6 = 16 km). The Fibonacci approximation also works: consecutive Fibonacci numbers (5, 8, 13, 21, 34, 55...) are near-perfect mile-to-km converters because the ratio approaches the golden ratio (1.618), close to 1.609. So 5 miles ≈ 8 km, 8 miles ≈ 13 km, etc. For fuel economy, US cars rate in miles per gallon (mpg) while most countries use liters per 100 km (L/100km): divide 235.215 by mpg to convert.

A US fluid ounce = 29.5735 mL, while an Imperial (UK) fluid ounce = 28.4131 mL — the US ounce is about 4% larger. This seems small, but it compounds at higher volumes: a US gallon (128 fl oz) = 3,785.41 mL while an Imperial gallon (160 fl oz) = 4,546.09 mL — the Imperial gallon is about 20% larger. When following British or Australian recipes, a "cup" means 250 mL (metric cup), not 236.6 mL (US cup) or 284 mL (Imperial cup). This 5-14% difference can significantly affect baking results where precision matters. The split originated in 1824 when the UK redefined its gallon based on the volume of 10 pounds of water at 62°F, while the US retained the pre-1824 English wine gallon (231 cubic inches). This calculator uses US Customary units — check labels carefully when using international recipes.

The formula is °C = (°F − 32) × 5/9. Reverse: °F = (°C × 9/5) + 32. Key reference points: 32°F = 0°C (water freezes), 72°F = 22.2°C (comfortable room temperature), 98.6°F = 37°C (normal body temperature), 212°F = 100°C (water boils at sea level), 350°F = 176.7°C (common baking temperature), −40°F = −40°C (the unique crossover point where both scales equal). Quick mental estimate: subtract 30, then divide by 2 — gives results within ±3°C for everyday temperatures (70°F → (70−30)/2 = 20°C, actual = 21.1°C). For weather: 0°C is freezing, 10°C is cool jacket weather, 20°C is pleasant, 30°C is hot, 40°C is dangerously hot. Kelvin (used in science) adds 273.15 to Celsius: 0°C = 273.15 K, −273.15°C = 0 K (absolute zero). Check your temperature with the BMI Calculator which includes health reference temperatures.

Exactly 16 US cups = 1 US gallon. The full US Customary liquid volume chain: 2 tablespoons = 1 fluid ounce, 8 fluid ounces = 1 cup, 2 cups = 1 pint, 2 pints = 1 quart, 4 quarts = 1 gallon. So 1 gallon = 128 fluid ounces = 3,785.41 mL = 3.785 liters. Practical conversions for cooking: 1 cup = 48 teaspoons = 16 tablespoons = 236.6 mL. For water weight: 1 gallon of water weighs approximately 8.34 lb (3.785 kg) at room temperature — helpful for calculating water transport weight (a 5-gallon jug weighs ~41.7 lb). Metric equivalents: most of the world uses 250 mL as a "metric cup" (slightly larger than the US 236.6 mL cup). These differences matter for recipe scaling — halving or doubling recipes requires accurate base measurements.

1 pound (lb) = 0.45359237 kilograms (kg) exactly — this is the international avoirdupois pound defined by the 1959 International Yard and Pound Agreement, signed by the US, UK, Canada, Australia, New Zealand, and South Africa. For quick estimation: divide pounds by 2.2 (or multiply kg by 2.2 to get pounds). Examples: 150 lb = 68.04 kg, 200 lb = 90.72 kg, 100 kg = 220.46 lb. Note the distinction: 1 avoirdupois pound (everyday use) = 16 ounces = 453.592 g, while 1 troy pound (precious metals) = 12 troy ounces = 373.242 g. The avoirdupois system is used for body weight, groceries, shipping, and industrial measurement in the US. Check your weight in both systems with the BMI Calculator, which handles automatic lb↔kg conversion.

1 acre = 43,560 square feet exactly (4,046.86 m² or 0.4047 hectares). The acre was historically defined as the area a team of oxen could plow in one day — a strip 1 furlong (660 ft) long by 1 chain (66 ft) wide = 43,560 sq ft. Size context: a standard American football field (excluding end zones) is approximately 1.1 acres. An NBA basketball court is 0.108 acres. The typical US suburban lot is 0.15–0.25 acres (6,500–10,900 sq ft). In real estate, price-per-acre varies enormously: rural farmland averages $3,800/acre nationally (USDA 2024), while commercial land in Manhattan can exceed $300 million/acre. For property tax calculations on your lot, see the Paycheck Calculator to understand how SALT deductions affect your take-home pay.

Yes — all conversion factors are sourced from NIST Special Publication 811 and Handbook 44, the official US measurement standards. Length conversions use the 1959 International Yard and Pound Agreement: 1 inch = 25.4 mm exactly (not approximately), 1 pound = 0.45359237 kg exactly. Temperature formulas use the precise thermodynamic definitions: °C = (°F − 32) × 5/9 and K = °C + 273.15. Volume conversions use NIST-defined US Customary measures based on the 1 gallon = 231 cubic inches definition. The only conversions that involve approximation are those between unrelated unit systems (e.g., nautical miles to statute miles, where 1 NM = 1.852 km exactly by international agreement, but the statute mile relationship is 1 NM = 1.15078 statute miles). Floating-point display may round beyond 10 decimal places, but the underlying calculation uses full precision.

The US actually uses the US Customary system, not Imperial — the two diverged after American independence. The main reason for continued use: cost, culture, and inertia. The Metric Conversion Act of 1975 (P.L. 94-168) made metric adoption voluntary, and without a mandate, widespread conversion never happened. Converting all 4 million miles of road signs, millions of engineering drawings, building codes, tool sizes, and public understanding would cost an estimated $300+ billion. NASA famously lost the $125 million Mars Climate Orbiter in 1999 due to a metric/imperial unit confusion. Despite this, metric is already the legal standard for US science (NIST), medicine (FDA dosages in mg/mL), military (distances in km, ammunition in mm), international trade (Omnibus Trade Act 1988), and nutrition labels (grams/mL required by 21 CFR 101). Only 3 countries have not officially adopted metric: the US, Myanmar, and Liberia.

A troy ounce = 31.1035 grams, while a regular (avoirdupois) ounce = 28.3495 grams — the troy ounce is approximately 9.7% heavier. Troy weight is exclusively used for precious metals: when gold is quoted at "$2,350 per ounce," that means per troy ounce. One troy pound = 12 troy ounces (373.2g), versus 1 avoirdupois pound = 16 ounces (453.6g) — so a troy pound is actually lighter than a regular pound despite each troy ounce being heavier. This matters for investors: buying "1 ounce of gold" means 31.1g, not 28.3g. If a jeweler prices a gold chain at "$85 per ounce" using avoirdupois instead of troy, they are undercharging by 9.7%. The COMEX (commodity exchange) and London Bullion Market both price in troy ounces. Silver ($28/troy oz), platinum ($970/troy oz), and palladium also use troy weight.

The top conversions for US property and construction: 1 acre = 43,560 sq ft (lot sizing — a typical suburban lot is 0.15–0.25 acres). 1 square foot = 0.0929 m² (international buyers need this). Board foot = 144 cubic inches (lumber pricing — a 2×4×8 board = 5.33 board feet). 1 yard of concrete = 1 cubic yard = 27 cubic feet = 0.765 m³ (approximately $150–$180 per yard in 2026). R-value per inch varies by insulation type: fiberglass batt R-3.2, spray foam R-6.5, rigid foam R-5.0 (per inch of thickness). Roofing uses "squares" — 1 square = 100 sq ft of roof area. A 2,000 sq ft home footprint with average roof pitch needs approximately 25 squares of shingles. For property tax, assessors use square footage — verify your home's measured area matches county records. See how property size affects taxes with the Paycheck Calculator (SALT deduction impact).

The metric system uses a consistent set of power-of-10 prefixes that apply to any base unit. Key prefixes: nano (n) = 10⁻⁹, micro (μ) = 10⁻⁶, milli (m) = 10⁻³, centi (c) = 10⁻², kilo (k) = 10³, mega (M) = 10⁶, giga (G) = 10⁹, tera (T) = 10¹². So 1 kilometer = 1,000 meters, 1 megabyte = 1,000 kilobytes (in SI; computing uses 1,024). Common applications: medicine uses milligrams (mg) and micrograms (μg) — a 500 mg aspirin = 0.5 g. Internet speed uses megabits per second (Mbps) — 1 Gbps = 1,000 Mbps. Storage uses terabytes (TB) — 1 TB = 1,000 GB = 1,000,000 MB. Energy bills use kilowatt-hours (kWh) — the average US home uses ~900 kWh/month. Convert between any metric prefixes by simply moving the decimal point.