1. Length conversion factors
1 in = 25.4 mm; 1 ft = 12 in; 1 yd = 3 ft; 1 mi = 5280 ft; 1 m = 100 cm
Accessible text: one inch equals twenty-five point four millimeters. One foot equals twelve inches. One yard equals three feet. One mile equals five thousand two hundred eighty feet. One meter equals one hundred centimeters.
Plain English: map both units to meters, then to the destination. Metric prefixes move the decimal point. Customary units rest on the international inch.
Worked example: 12 in × 2.54 = 30.48 cm. Open it in the length converter.
Limitation: JavaScript Number is not arbitrary-precision arithmetic. Very large kilometer products may round.
2. Mass conversion factors
1 lb = 0.45359237 kg; 1 oz = 1/16 lb; 1 t = 1000 kg; 1 US short ton = 2000 lb
Accessible text: one avoirdupois pound equals zero point four five three five nine two three seven kilograms exactly. One ounce is one sixteenth of a pound. One metric tonne is one thousand kilograms. One US short ton is two thousand pounds.
Plain English: mass conversions are multiplication. Everyday “weight” language still uses these mass units here. Gravity is not involved.
Worked example: 10 lb × 0.45359237 = 4.5359237 kg. Use the weight and mass converter.
Limitation: troy ounces are not offered. US short tons are not metric tonnes.
3. Temperature formulas
°F = (°C × 9/5) + 32; °C = (°F − 32) × 5/9; K = °C + 273.15
Accessible text: Fahrenheit equals Celsius times nine-fifths plus thirty-two. Celsius equals Fahrenheit minus thirty-two, times five-ninths. Kelvin equals Celsius plus two hundred seventy-three point one five.
Plain English: temperature scales do not share a zero. An offset is required. Do not multiply by a single length-style factor.
Worked example: 25 °C → (25 × 9/5) + 32 = 77 °F. Use the temperature converter.
Limitation: values below absolute zero are rejected. Kelvin cannot be negative.
4. Volume conversions
1 US gal = 3.785411784 L; 1 US cup = 1/16 gal; 1 US fl oz = 1/128 gal
Accessible text: one US gallon equals three point seven eight five four one one seven eight four liters exactly. One US cup is one sixteenth of a US gallon. One US fluid ounce is one one-hundred-twenty-eighth of a US gallon.
Plain English: cooking units on this site are US customary. They are not imperial gallons and not 250 mL metric cups.
Worked example: 2 US cups = 473.176473 mL. Use the volume converter.
Limitation: household cups are approximate compared with laboratory glassware. Volume is not mass.
5. Area conversion factors
1 ft² = 0.3048² m² = 0.09290304 m²; 1 ha = 10,000 m²; 1 acre = 43,560 ft²
Accessible text: one square foot equals zero point zero nine two nine zero three zero four square meters. One hectare equals ten thousand square meters. One acre equals forty-three thousand five hundred sixty square feet.
Plain English: square the linear factor. Converting feet to meters with 0.3048 and reusing that number for square feet is wrong.
Worked example: 100 ft² × 0.09290304 = 9.290304 m². Use the area converter.
Limitation: legal land units are defined independently of a household tape measure’s rounding.
6. Speed conversion factors
1 mph = 0.44704 m/s; 1 km/h = 1/3.6 m/s; 1 kn = 1852 m/h
Accessible text: one mile per hour equals zero point four four seven zero four meters per second. One kilometer per hour equals one divided by three point six meters per second. One knot equals one thousand eight hundred fifty-two meters per hour.
Plain English: speed is length over time. Convert both parts, or use a combined factor to meters per second.
Worked example: 60 mph × 1.609344 = 96.56064 km/h. Use the speed converter.
Limitation: this is not a live speed measurement and does not read GPS or vehicle sensors.
7. Time conversions
1 min = 60 s; 1 h = 60 min; 1 d = 24 h; 1 wk = 7 d; 1 s = 1000 ms
Accessible text: one minute equals sixty seconds. One hour equals sixty minutes. One day equals twenty-four hours. One week equals seven days. One second equals one thousand milliseconds.
Plain English: these durations are fixed clock units. Calendar months and years are not fixed, so they are omitted.
Worked example: 90 min ÷ 60 = 1.5 h. Use the time converter.
Limitation: leap seconds and civil date arithmetic are outside this converter.
8. Decimal and binary storage units
1 B = 8 bit; 1 kB = 1000 B; 1 KiB = 1024 B; 1 GB = 10⁹ B; 1 GiB = 2³⁰ B
Accessible text: one byte equals eight bits. One kilobyte equals one thousand bytes. One kibibyte equals one thousand twenty-four bytes. One gigabyte equals one billion bytes. One gibibyte equals two to the thirtieth bytes.
Plain English: SI prefixes are decimal. IEC prefixes are binary. Mixing them is why a “1 GB” file and a “1 GiB” report disagree.
Worked example: 1 GB = 1,000,000,000 / 1,073,741,824 GiB ≈ 0.931322575 GiB. Use the digital storage converter.
Limitation: disk formatting overhead is not a unit conversion.
See also conversion charts and how to convert units of measurement.