Convert units across 20+ categories with precise rounding, batch mode, and scientific notation support. Convert length, mass, temperature (°C/°F/K), volume, area, data (MB vs MiB), speed, pressure, energy, and time units.
Scientific Accuracy Standards
This converter uses NIST-standard constants and exact conversion factors where applicable. Temperature conversions include proper offset handling. For critical applications, verify results match your specific standards and reporting requirements.
Select a category and units to start converting between different measurements.
A dimension is a measurable physical quantity like length, mass, or time. A unit is a standardized reference for expressing that dimension—for example, meters and feet are both units of length. This converter supports 20+ categories (dimensions), each with multiple units from different measurement systems.
The International System of Units (SI/Metric) uses base-10 scaling and standardized prefixes (kilo-, mega-, giga-) for consistency. Most countries use metric for science, engineering, and daily life. The US Customary/Imperial system (feet, pounds, gallons) evolved from historical British units and uses non-decimal relationships (12 inches = 1 foot, 16 ounces = 1 pound). The US is one of only three countries not officially metric, though scientific work worldwide uses SI.
Conversions between systems use exact or conventional constants. For example, 1 inch is exactly 25.4 millimeters by international definition (1959 treaty). However, some constants like pound-to-kilogram (1 lb = 0.45359237 kg) were originally empirical and standardized later for global consistency.
SI prefixes scale units by powers of 10. Common prefixes include:
These prefixes apply uniformly across dimensions. Converting within the same system (e.g., kilometers to meters, gigabytes to megabytes) is simple base-10 arithmetic. Converting between systems (e.g., miles to kilometers) requires a conversion factor.
Temperature conversions are unique because they involve both scaling and offset adjustments. Most dimensions (length, mass, volume) use simple multiplication: 5 feet × 0.3048 = 1.524 meters. Temperature requires formulas:
Example: 100°C (boiling water) = 212°F = 373.15 K. Notice 0°C ≠ 0°F (it equals 32°F), and 0 K (absolute zero) = −273.15°C = −459.67°F. Kelvin has no "degrees" symbol and no negative values—it's an absolute scale starting at absolute zero.
This converter offers configurable precision (0-8 decimal places) and rounding modes (normal, floor, ceiling). Precision determines how many decimal places appear in results. Rounding modes control edge cases:
In engineering and science, significant figures represent measurement precision. If you measure 5.2 meters (2 sig figs), converting to feet gives 17.06 feet, but you should report ~17 feet (2 sig figs) to match original precision. This converter displays calculated values—you're responsible for rounding to match your measurement precision.
Some conversions use exact definitions (e.g., 1 inch = 25.4 mm exactly, defined by treaty). Others use conventional constants maintained by standards bodies like NIST (National Institute of Standards and Technology). For example, the speed of light is exactly 299,792,458 m/s by definition (the meter is now defined in terms of the speed of light), while the gravitational constant G is measured empirically and has uncertainty.
This converter uses NIST-standard constants where applicable, ensuring consistency with scientific and engineering practice. For critical applications (aerospace, pharmaceuticals, legal metrology), verify that our constants match your specific industry standards or regulatory requirements.
Data storage has two competing standards that cause widespread confusion:
This discrepancy explains why a "500 GB" hard drive shows as 465 GB in Windows: the manufacturer used decimal (500,000,000,000 bytes), but Windows displays binary GiB labeled as "GB" (500,000,000,000 ÷ 1,073,741,824 ≈ 465 GiB). This converter supports both standards—use MB/GB for marketing specs and MiB/GiB for actual memory calculations.
This converter is designed for both quick everyday conversions and advanced engineering calculations with batch processing. Follow these steps to get accurate results:
Pro Tip: For engineering work, use the precision slider to match your measurement instrument's accuracy. If your ruler measures to 0.1 mm, set 1 decimal place. For scientific notation input, use "e" notation: 3.5e6 = 3,500,000, 1.2e-3 = 0.0012.
Some quantities combine dimensions. Speed is length/time (miles per hour, meters per second). Density is mass/volume (grams per cubic centimeter). Pressure is force/area (pounds per square inch, pascals). Make sure you're converting within the correct compound category—converting MPH to meters won't give you m/s (you need the speed category).
When converting a temperature value (e.g., "it's 20°C outside"), use the full formula with offset: 20°C = 68°F. But when converting a temperature difference or interval (e.g., "the temperature rose 10°C"), use only the scaling: 10°C change = 18°F change (multiply by 9/5, no offset). This converter handles value conversions—for differences, manually multiply: ΔF = ΔC × 9/5.
Converting kilometers to meters? Multiply by 1,000 (kilo- = 10³). Megabytes to bytes? Multiply by 1,000,000 (mega- = 10⁶). Milliseconds to seconds? Divide by 1,000 (milli- = 10⁻³). Once you know prefixes, you can convert within SI instantly: 5 gigawatts = 5,000 megawatts = 5,000,000 kilowatts = 5,000,000,000 watts.
When converting file sizes or memory, check whether your source uses decimal (MB) or binary (MiB). RAM specs use binary (16 GiB = 17.18 GB). Hard drive labels use decimal (2 TB = 2,000 GB). Cloud storage often uses decimal. If you're calculating how many files fit on a drive, use the same standard as the drive manufacturer (usually decimal). If you're programming memory allocation, use binary.
If you're cutting material and can't exceed a dimension (safety clearance, material limits), use floor rounding. If you're sizing a container and need to ensure everything fits, use ceiling rounding. For statistical analysis or when accuracy matters more than bias, use normal (half-up) rounding. Example: cutting 10-foot boards into 3.2-meter lengths. 10 ft = 3.048 m. You can cut 0 full 3.2 m lengths (3.048 ÷ 3.2 = 0.9525, floor = 0). Use floor to avoid overestimating material yield.
If you're converting a list of measurements (e.g., recipe ingredients, parts dimensions, survey distances), use batch mode. Paste values from Excel/Sheets as comma-separated (or tab-separated) and convert all at once. Export as CSV to re-import into your original file. This is far faster and less error-prone than converting one at a time.
Many units have multiple names or abbreviations. Length: m (meters), ft (feet), in (inches), yd (yards), mi (miles), km (kilometers), cm (centimeters). Volume: L (liters), gal (gallons), ml (milliliters), fl oz (fluid ounces), qt (quarts). This converter recognizes standard abbreviations—if unsure, check the dropdown or type the full name.
The US and UK use different definitions for some Imperial units. A US gallon is 3.785 liters, but a UK (Imperial) gallon is 4.546 liters. A US ton (short ton) is 2,000 pounds, but a UK ton (long ton) is 2,240 pounds. A metric ton (tonne) is 1,000 kilograms (2,204.62 pounds). Always specify which system you're using—this converter labels units clearly (US gal, UK gal, metric ton).
For aerospace, pharmaceuticals, legal metrology, or safety-critical engineering, verify that our conversion constants match your specific standards (NIST, ISO, ASTM, regulatory requirements). While we use NIST-standard values, different industries sometimes use slightly different conventional constants or require specific rounding procedures mandated by regulation.
Unit conversions appear in countless real-world scenarios—from cooking and home improvement to international travel and professional engineering. Understanding when and how to convert units accurately saves time, prevents costly errors, and improves decision-making:
Pro Tip: For any real-world conversion, verify you're using the right category (length vs area vs volume vs mass). Determine whether precision matters (engineering yes, casual cooking no), and always round appropriately for the context—ceiling for material purchasing, floor for maximum dimensions, normal for statistical analysis. Batch mode saves time for large datasets; use it for recipe scaling, construction material lists, or converting spec sheets.
Even experienced professionals make unit conversion errors. Recognizing these common pitfalls prevents costly mistakes, safety hazards, and project failures:
The pattern across these mistakes: assumptions without verification, manual arithmetic errors, and context mismatches. Prevention strategies: (1) Always use dedicated conversion tools (this converter) instead of manual math for non-trivial conversions. (2) Verify units match source and destination requirements (US vs metric, decimal vs binary, absolute vs relative). (3) Check dimensional analysis (units cancel correctly). (4) Sanity-check results (order of magnitude, intuitive direction). (5) For critical applications (engineering, medical, legal), have a second person verify conversions. A $50 material shortage from conversion error can cost $500 in rush shipping and schedule delays. A 10% torque error can cause equipment failure. The time spent verifying conversions pays for itself many times over.
Results display in your selected precision (0-8 decimal places) with the target unit symbol. For example, converting 5 miles to kilometers with 3 decimal places shows "8.047 km". The precision setting doesn't affect calculation accuracy (internally we use full floating-point precision)—it only affects displayed rounding.
Below your result, you'll see the conversion factor: "1 mile = 1.609344 kilometers". This is the multiplier used in the conversion. You'll also see the inverse: "1 kilometer = 0.621371 miles". The inverse is useful for quick mental checks (if 1 km ≈ 0.62 mi, then 10 km ≈ 6.2 mi, 100 km ≈ 62 mi).
For extremely large or small numbers, results display in scientific notation. Example: 1 light-year = 9.461e15 meters (9.461 trillion meters). This prevents unwieldy displays like "9,461,000,000,000,000". You can input values in scientific notation too: type "1.5e6" for 1,500,000.
Temperature results use the full offset formula. Converting 0°C shows 32°F (not 0°F), because the formula is °F = (0 × 9/5) + 32. Negative temperatures are common (−40°C = −40°F is the same temperature; below that, Celsius is "warmer" than the Fahrenheit number). Kelvin never goes negative because it's an absolute scale starting at absolute zero (0 K = −273.15°C).
In batch mode, results display as a table with columns: Original Value, Original Unit, Converted Value, Converted Unit. You can copy the entire table to paste into spreadsheets, or export as CSV for data analysis. CSV format uses commas to separate columns and includes a header row.
This converter normalizes unit symbols to standard abbreviations. You might type "kilometers", but the result shows "km". Fahrenheit appears as "°F" (with degree symbol), Celsius as "°C", Kelvin as "K" (no degree symbol). This follows international standards (SI, ISO) for scientific notation.
Rounding only affects the displayed result, not intermediate calculations. If you convert 10 miles to kilometers (16.09344 km), then convert that result to meters, we calculate 10 mi → m directly (16,093.44 m), not 16.09344 → m (which would lose precision). This prevents cumulative rounding errors in multi-step conversions.
Conversion factors come from NIST Special Publication 811, ISO standards, and international treaty definitions (like the 1959 international yard/pound agreement). We update constants when standards bodies issue revisions. For the most critical applications, check that the version date of constants matches your requirements.
Why isn't 0°C = 0°F? Because they have different zero points. 0°C is freezing water, 32°F is freezing water.
Why does my 500 GB drive show as 465 GB? Manufacturer used decimal GB (base-10), OS shows binary GiB labeled as "GB".
Why is 1 US gallon ≠ 1 UK gallon? Different historical definitions. Always specify which gallon.
Why does 1 inch = 2.54 cm exactly, not 2.54000001? It's an exact definition by international treaty.
If a result looks unexpected, double-check that you're using the right category, the right system (US vs UK vs SI), and the right conversion type (absolute vs relative for temperature).
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