The calculation model
For ordinary linear conversions, Unitwise first turns the entered value into the category’s base unit. It then converts that base value into the selected result unit. This avoids chaining together several rounded conversions.
base value = entered value × source factor
result = base value ÷ destination factor
For example, kilometers and miles both pass through meters. Five kilometers becomes 5,000 meters; dividing by 1,609.344 meters per mile gives approximately 3.106855961 miles.
References
Physical conversion factors are based primarily on the U.S. National Institute of Standards and Technology’s Guide to the SI, Appendix B, including the tables organized alphabetically and by quantity. NIST describes Appendix B as an essential source when exact conversion factors are required.
Digital decimal and binary prefixes follow NIST’s binary-prefix definitions. In particular, decimal prefixes use powers of 1,000 while binary prefixes use powers of 1,024.
Base units by category
| Category | Base unit | Notes |
|---|---|---|
| Length | meter (m) | International inch, foot, yard, and mile |
| Weight & mass | kilogram (kg) | Avoirdupois ounce and pound |
| Temperature | kelvin (K) | Uses scale-specific formulas |
| Volume | liter (L) | U.S. customary cooking and liquid units |
| Area | square meter (m²) | Derived from exact length factors |
| Speed | meter per second (m/s) | International nautical mile for knots |
| Time | second (s) | Year is fixed at 365.25 days |
| Digital storage | byte (B) | Includes decimal and binary prefixes |
| Energy | joule (J) | Thermochemical calorie and IT Btu |
| Pressure | pascal (Pa) | Standard atmosphere is 101,325 Pa |
Temperature is different
Celsius, Fahrenheit, and kelvin do not share the same zero point. A multiplier alone is therefore not enough. Unitwise uses these equations:
°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9
K = °C + 273.15
The calculator rejects temperature values below absolute zero: 0 K, −273.15 °C, or −459.67 °F.
Selected exact and defined factors
| Unit | Base equivalent |
|---|---|
| 1 inch | 0.0254 meter |
| 1 foot | 0.3048 meter |
| 1 international mile | 1,609.344 meters |
| 1 nautical mile | 1,852 meters |
| 1 pound | 0.45359237 kilogram |
| 1 U.S. gallon | 3.785411784 liters |
| 1 acre | 4,046.8564224 square meters |
| 1 standard atmosphere | 101,325 pascals |
| 1 kilowatt-hour | 3,600,000 joules |
Decimal and binary data
Decimal storage units are based on powers of ten: 1 kB is 1,000 bytes, 1 MB is 1,000,000 bytes, and 1 GB is 1,000,000,000 bytes. Binary units are based on powers of two: 1 KiB is 1,024 bytes, 1 MiB is 1,048,576 bytes, and 1 GiB is 1,073,741,824 bytes.
Why it matters: a drive marketed as 1 TB contains 1,000,000,000,000 bytes, which is about 931.3 GiB. The number changes because the unit changes—not because storage disappeared.
Volume convention
Unitwise currently includes U.S. customary teaspoons, tablespoons, fluid ounces, cups, pints, quarts, and gallons. It does not silently substitute Imperial equivalents. The same unit name can describe a different volume in another system, so every ambiguous volume unit is labeled “US” in the selector.
Precision and rounding
Calculations are performed with standard JavaScript double-precision floating-point numbers. The interface displays up to ten significant digits for readability, while editable result fields retain up to eleven significant digits. Very large or very small results may appear in scientific notation.
Displayed precision is not measurement certainty. If a trip was measured as 5 miles to the nearest mile, a conversion with many decimals does not make the original estimate more exact. Round the final answer to a precision appropriate for your source and purpose.
Limits of use
Unitwise is designed for everyday reference and educational use. Do not treat it as a calibration service or as a substitute for required standards, verified software, professional judgment, or independent checking in medical, scientific, engineering, legal, trade, or safety-critical work.
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