What the converter hub covers How to use it 01 Pick a category. The strip holds all thirteen names; arrow keys move along it. Currency opens the live-rate panel, the other twelve the unit cards. 02 Choose the units. Each card has a dropdown of the category's units and shows the chosen symbol beneath. The cards sit side by side on wide screens and stack on narrow ones. 03 Type on either card. The other card converts as you type, and the All Units list repeats the value in every unit. The swap button exchanges the units and carries the value across. 04 Type an expression when one number is not enough. The focused field evaluates arithmetic: 90/2 shows a quiet = 45 hint and converts the running value; Enter settles the field to 45. An unfinished 90+ shows = ? and keeps the last settled value. 05 Use the list and the keypad. Click any All Units row to move that unit to the focused card; the keypad button opens a standard calculator. Worked readouts Every readout below is exactly what the hub displays.
Category
Enter
Displayed readout
Length
1 mi → km
1.609344 km ; list: 5,280 ft , 63,360 in , 0.8689762419 nmi
Length
90/2 in the mi cardhint = 45; 72.42048 km ; Enter settles the card to 45
Weight
1 kg → lb
2.2046226219 lb ; list: 35.2739619496 oz , 0.001 t
Weight
1 lb → g
453.59237 g ; 0.45359237 kg , 2,267.96185 ct
Volume
1 gal (US) → L
3.785411784 L ; 3,785.411784 mL , 231 in³ , 0.8326741846 imp gal
Temperature
98.6 °F → °C
37 °C , 310.15 K ; 37 °C returns 98.6 °F
The right card works the same way: 10 mi reads 16.09344 km , 5 km reads 3.1068559612 mi .
How the categories relate Each category is one quantity, and its units differ only by size — except temperature, where Celsius, Fahrenheit, Kelvin and Rankine also differ by an offset. Length resolves to the metre, weight to the kilogram, volume to the millilitre. The factors are exact definitions: 1 in = 25.4 mm and 1 lb = 0.45359237 kg were fixed by the 1959 yard-and-pound agreement, and the US gallon is 231 in³ = 3.785411784 L; the imperial gallon is a separate statute at 4.54609 L. Temperature is affine: 0 °C reads 32 °F and 100 °C 212 °F .
Display and scope
Twelve significant digits, capped at ten decimals. Between 10⁻¹⁰ and 10¹⁵ results print with comma grouping and at most 10 decimal places; outside that band they use exponential form with six decimals. 1 kg shows 2.2046226219 lb rather than the longer 2.20462262185, and the light-year row for 1 mi reads 1.701078e-13 ly .
One category at a time. Switching category loads its first two units and the value 1; the pair and the typed number do not follow you across the strip. No cross-category or formula conversion. It never converts weight to volume, energy to power or speed to time — each needs a density, a duration or another input — and the focused field evaluates arithmetic (90/2, (1+2)*3), not functions. Enter the formula on the scientific calculator . Ounce and gallon traps
An ounce is not a fluid ounce. The Weight category's ounce is mass: 1 oz reads 28.349523125 g . The Volume category's fluid ounce is volume: 1 fl oz reads 29.5735295625 mL , eight of them to one US cup. The numbers are close; the quantities are not.A gallon depends on the flag. One US gallon is 3.785411784 L and 0.8326741846 imp gal ; one imperial gallon is 4.54609 L , about 20% larger. Where it fits Cooking and labels A US recipe cup is 236.5882365 mL and a US fluid ounce 29.5735295625 mL ; the All Units list turns either into tablespoons — 1 cup reads 16 tbsp , 1 fl oz 2 tbsp .
Travel and distance A 5 km race is 3.1068559612 mi and a 10 mi drive is 16.09344 km ; the same entry also reads out in feet, yards and nautical miles.
Body and weather 98.6 °F is 37 °C , 0 °C is 32 °F , and 100 °C is 212 °F ; the Kelvin and Rankine rows cover the absolute scales.
Privacy All input and calculation run inside your browser and are never uploaded; this page is static text and records no user input.
References
BIPM, The International System of Units (SI Brochure) , 9th edition — the base units and prefixes behind the metre, kilogram, second and kelvin, and the distinction between quantities and units. bipm.org （访问日期：2026-10-01）
NIST Special Publication 811, Appendix B.8, Factors for Units Listed Alphabetically — the exact factors for the inch, pound, US gallon and US fluid ounce used by the converter. nist.gov （访问日期：2026-10-01）
Wikipedia, Fluid ounce — the US and imperial fluid ounce, and why a fluid ounce measures volume rather than weight. en.wikipedia.org （访问日期：2026-10-01）
Wikipedia, International yard and pound — the 1959 agreement that fixed 1 yd = 0.9144 m and 1 lb = 0.45359237 kg. en.wikipedia.org （访问日期：2026-10-01）
Calculators in this hub
Hand-picked tools, one click away. The mini versions compute live and carry your values into the full calculator.
Sources & review
Reviewed by CalcX Editorial Team
Updated 2026-10-01 BIPM, The International System of Units (SI Brochure), 9th edition — the base units and prefixes behind the metre, kilogram, second and kelvin, and the distinction between quantities and units (accessed 2026-10-01) NIST Special Publication 811, Appendix B.8, Factors for Units Listed Alphabetically — the exact factors for the inch, pound, US gallon and US fluid ounce used by the converter (accessed 2026-10-01) Wikipedia, Fluid ounce — the US and imperial fluid ounce, and why a fluid ounce measures volume rather than weight (accessed 2026-10-01) Wikipedia, International yard and pound — the 1959 agreement that fixed 1 yd = 0.9144 m and 1 lb = 0.45359237 kg (accessed 2026-10-01)