UnitSwap is a unit converter that covers over 200 units spread across 17 categories. Length, weight, temperature, volume -- those are the obvious ones. But it also handles less common conversions like torque, typography points, fuel economy, and data storage. Ever needed to convert Newton-meters to foot-pounds? Or picas to millimeters for a print layout? That is the kind of thing most converters skip, and the kind of thing you inevitably need at 11pm on a deadline.
Every conversion shows the formula used, so you are not just getting a magic number. You can see exactly how the calculation works, which is useful for double-checking homework, verifying engineering specs, or just satisfying your curiosity about why there are 5,280 feet in a mile (blame medieval English farmers, essentially).
Start by selecting a category from the pills at the top -- Length, Weight, Temperature, and so on. The From and To dropdowns update to show the available units in that category. Type a value into either field and the other updates in real time. You can also type directly into the result field to do a reverse conversion.
The Quick Reference table (collapse it if you find it distracting) shows common conversions for whatever category you have selected. Need to know how many tablespoons are in a cup without running a conversion? It is right there. The swap button between the From and To fields flips the direction instantly, which saves a surprising amount of clicking when you are converting back and forth repeatedly.
UnitSwap runs entirely in your browser with no server calls whatsoever. All 200+ conversion formulas are baked into the JavaScript that loads with the page. There is no API, no database query, no telemetry on what you convert. Type in classified rocket propulsion figures if you want to -- we genuinely have no mechanism to see them.
UnitSwap uses standard conversion factors defined by international measurement bodies (SI, NIST, ISO). For temperature, we apply the exact formulas (not approximations) for Celsius, Fahrenheit, Kelvin, and Rankine. Floating-point precision in JavaScript gives you about 15 significant digits, which is more than sufficient for any practical use case.
There are 17 categories: Length, Weight/Mass, Temperature, Volume, Speed, Area, Time, Data Storage, Pressure, Energy, Power, Frequency, Angle, Fuel Economy, Force, Torque, and Typography. Each contains between 6 and 20 individual units.
No. Cross-category conversions (such as grams to milliliters) depend on the density of the specific substance, which varies. UnitSwap handles pure unit-to-unit conversions within each category, where the relationship is fixed and universal.
Most unit conversions are linear — multiply by a constant and you're done. Temperature is different because the scales don't share a common zero point. Celsius and Fahrenheit have different-sized degrees AND different starting points (water freezes at 0°C but 32°F). So converting requires both multiplication and addition: °F = (°C × 9/5) + 32. Kelvin is simpler — it's just Celsius shifted by 273.15 — but Rankine, Réaumur, and the other scales in this tool each have their own offset formulas.
The tool uses JavaScript's native floating-point arithmetic (64-bit IEEE 754), which gives you about 15-16 significant digits of precision. For everyday use — cooking, construction, travel — that's far more precision than you'll ever need. For scientific or engineering work requiring arbitrary precision, you might want to verify critical calculations with a specialized library, but for unit conversion the standard floating-point math is more than adequate.
Yes — astronomical (light-years, parsecs), nautical (knots, fathoms), historical (furlongs, chains), and cooking (cups, tablespoons, pinches). 17 categories total.
US (29.57 mL) and Imperial (28.41 mL) are actually different volumes. The gap grows with larger measures — gallons differ by about 20%. The tool lists both variants separately.
Most conversions are simple multiplication. Temperature scales have different zero points AND different degree sizes, requiring both multiplication and addition. The tool handles all 8 temperature scales correctly.
Each category (length, weight, temperature, etc.) is a separate converter, so you’d do one conversion at a time. But the tool remembers your last selection in each category, so switching between them is fast. If you’re working on a project that involves multiple types of conversions — say, cooking with international recipes where you need both temperature and volume conversions — keep the tab open and flip between categories as needed.
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