Unit Converter

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Category:

Pick an everyday, engineering, digital, or fuel category; each category keeps source and target units compatible.

Source measurement:

The conversion updates immediately and keeps full precision before display rounding.

Target unit:

The all-unit table still lists every unit in the selected category.

Direction helper:

Use the same source number when checking the opposite direction.

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Display precision:

Calculations keep full numeric precision; this setting changes only output rounding.

Number notation:

Use Engineering or Scientific when comparing very small and very large unit scales.

Pair curve range:

Use Nearby for a local slope check; use Wide when comparing a broader practical range.

Unit list filter:

Filter by unit name, symbol, definition, or use case when a category has a long unit list.

Field	Value	Detail	Copy
{{ row.field }}	{{ row.value }}	{{ row.detail }}

Unit	Equivalent	Base definition	Best for	Copy
No unit rows match the current filter.
{{ row.unitLabel }}	{{ row.equivalentDisplay }}	{{ row.definition }}	{{ row.bestFor }}

Topic	Current reading	Use this note	Copy
{{ row.topic }}	{{ row.reading }}	{{ row.note }}

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Unit conversion keeps a measured quantity intact while expressing it with a different unit label. A package can be listed in inches or centimeters, a pump rating in gallons per minute or liters per minute, a storage size in GB or GiB, and a pressure reading in psi or kPa. The number changes because the unit size, reference scale, or inverse relationship changes.

The first practical decision is the measurement category. Length, area, volume, speed, force, torque, pressure, energy, and power all describe different physical quantities, even when some of their unit names look related. Feet and square feet cannot be mixed. A pound can mean mass in an everyday shipping note, while pounds-force belongs to force or torque. Fuel economy also needs care because distance-per-fuel units rise as efficiency improves, while fuel-per-distance units fall.

A source value converted through a base reference and displayed as a target unit

Reliable conversion usually passes through a reference unit for the category. Inches, feet, centimeters, and miles can all be normalized to meters before being expressed again. Digital storage needs a different kind of attention: decimal prefixes such as GB use powers of 1000, while binary prefixes such as GiB use powers of 1024. Data-rate units also separate bits from bytes, so Mbps and MB/s are not interchangeable labels.

A converted number should travel with its unit. The value 30.48 alone is not enough; 30.48 cm says what was measured. For temperatures, the unit is even more important because Celsius, Fahrenheit, kelvin, and Rankine have scale offsets or absolute references, not just larger or smaller unit sizes.

Technical Details:

Most measurement categories use multiplicative conversion. The source value is first converted to the category's base reference, then that base value is divided by the target unit's factor. This keeps the mathematical quantity stable while the displayed unit changes.

That factor rule works for ordinary units such as inches to centimeters and pounds to kilograms, but it also works for derived units such as square feet to square meters, cubic feet per minute to cubic meters per second, pound-force feet to newton meters, and kilowatt-hours to megajoules. The conversion remains a ratio as long as both units belong to the same category and neither unit requires a scale offset or inverse fuel-economy handling.

Formula Core:

The main multiplicative path uses a source factor and a target factor measured against the category's base reference.

V_{target} = \frac{V_{source} \times F_{source}}{F_{target}}

For 12 in to centimeters, the source factor is 0.0254 m per inch and the target factor is 0.01 m per centimeter. The base value is 0.3048 m, and the target value is 30.48 cm. Display precision rounds what is shown; it does not change the underlying numeric path before display.

Unit conversion categories and base references
Category	Base reference	Examples in the supported set	Main caution
Length	Meter	mm, cm, m, km, in, ft, yd, mi, nmi	Use distance units only; area and volume need their own categories.
Astronomical distance	Kilometer	km, mi, AU, ly, pc	Scientific or engineering notation is often easier for large space distances.
Weight / mass	Kilogram	mg, g, kg, oz, lb, st, ton, carat, troy ounce	Everyday weight labels are treated as mass quantities.
Temperature	Kelvin	deg C, deg F, K, deg R	Scale offsets apply, and values below 0 K are invalid.
Area	Square meter	cm2, m2, km2, ft2, yd2, acre, ha	Area factors come from squared length relationships.
Volume	Liter	mL, L, m3, US gal, US qt, US cup, US fl oz	US customary capacity units are separate from UK imperial capacity units.
Volume flow	Cubic meter per second	m3/s, m3/h, L/s, L/min, US gpm, CFM	US gallon rates use the US liquid gallon.
Speed	Meter per second	m/s, km/h, mph, ft/s, ft/min, kn	Knots are nautical miles per hour.
Acceleration	Meter per second squared	m/s2, cm/s2, ft/s2, mph/s, km/h/s, g	Standard gravity is an acceleration reference, not a mass unit.
Fuel economy	Kilometer per liter	km/L, mpg US, mpg Imp, mi/L, L/100 km, gal/100 mi	Consumption units invert the distance-per-fuel value and require a positive source value.
Time	Second	ns, us, ms, s, min, h, day, week, average month, average year	Average month and year values are fixed duration approximations, not date math.
Angle	Radian	rad, deg, turn, grad, arcmin, arcsec, NATO mil	Small angle units are angular subdivisions, not distance units.
Frequency	Hertz	Hz, kHz, MHz, GHz, rpm, bpm	RPM and BPM are treated as events per minute.
Force	Newton	N, kN, dyn, lbf, ozf, kgf	Kilogram-force is force under standard gravity, not mass.
Torque	Newton meter	N m, kN m, N cm, lbf ft, lbf in, kgf m	Torque is rotational moment; energy uses a separate category.
Pressure	Pascal	Pa, kPa, MPa, bar, atm, psi, Torr, mmHg, inHg	Absolute, gauge, and differential pressure can share unit labels but not meaning.
Energy	Joule	J, kJ, MJ, cal, kcal, Wh, kWh, BTU, eV	Food calories often mean kilocalories.
Power	Watt	W, kW, MW, hp, PS, BTU/h, TR	Power is energy rate; tons of refrigeration are cooling capacity.
Density	Kilogram per cubic meter	kg/m3, g/cm3, g/mL, kg/L, lb/ft3, lb/gal	US gallon density uses the US liquid gallon.
Digital storage	Byte	b, B, KB, KiB, MB, MiB, GB, GiB, TB, TiB	Decimal prefixes use powers of 1000; binary prefixes use powers of 1024.
Data rate	Bit per second	bps, Kbps, Kibps, Mbps, Mibps, B/s, MB/s, MiB/s	Bytes per second and bits per second differ by a factor of 8.

Special Conversion Rules:

Temperature and fuel economy need extra handling because their numbers do not behave like ordinary unit ratios. Temperature scales use offsets around kelvin. Fuel economy can express either distance per fuel or fuel consumed per distance, so some conversions invert the base value.

Special conversion rules for temperature and fuel economy
Case	Reference path	Boundary
Celsius to Fahrenheit	Convert deg C to K with +273.15, then express K as deg F.	Source values below -273.15 deg C are below 0 K.
Fahrenheit to Celsius	Convert deg F to K with an offset and 5/9 scale, then subtract 273.15.	Source values below -459.67 deg F are below 0 K.
Kelvin and Rankine	Kelvin is the base reference; Rankine uses Fahrenheit-sized absolute degrees.	Both absolute scales must stay at or above zero.
Fuel consumption	L/100 km and gal/100 mi are derived by inverting the km/L base value.	Zero or negative fuel-economy input cannot produce a valid result.

The Pair Range Curve plots source values against target values for the selected unit pair. Multiplicative conversions form a line through zero. Temperature conversions form a line with an offset. Fuel-consumption curves can move in the opposite direction from distance-per-fuel values because the relationship is inverse.

Everyday Use & Decision Guide:

Choose Category before entering the number. This prevents a common wrong answer: treating 100 ft2 as a length measurement or treating 10 lbf ft as energy. Once the category is correct, the source and target unit lists stay compatible with that measurement family.

Use Source measurement for the numeric value exactly as it appears in the source, then choose the source unit beside it. Target unit controls the large result at the top and the Target row in the Target Conversion tab. The Swap units button reverses the selected units while keeping the entered number, which is useful for checking the opposite direction without retyping.

Use Target Conversion when you need the main answer, base reference, formula path, display format, and guardrail message.
Use All Equivalent Units when a handoff needs several unit labels for the same source measurement.
Use Conversion Guidance when the category has a caveat, such as US gallon basis, absolute temperature, calendar averages, or decimal-versus-binary storage prefixes.
Use Pair Range Curve to inspect how nearby, wide, or zero-to-input source values move in the selected target unit.
Use Unit list filter to narrow a long all-unit table by unit name, symbol, definition, or use case.

The Display precision control changes visible decimals in the summary, tables, chart data, and JSON display values. It does not mean the source measurement is more accurate. If a source label says 2 cups, displaying six decimals can help a recipe audit, but it does not create laboratory precision.

Read the warning area before copying a result. Negative signed quantities may be mathematically converted, but negative length, area, volume, mass, pressure, energy, or power may not describe a physical measurement. For fuel economy, use a positive value. For temperature, values below absolute zero must be corrected before the result can be trusted.

Step-by-Step Guide:

Use this flow for a single conversion, then open the extra result tabs only when they help check or share the answer.

Set Category. The source and target unit lists should immediately change to units for that measurement family.
Enter the number in Source measurement and choose the source unit in the adjacent selector. Blank input is treated as 0; invalid numeric input is reset to the category default and produces a warning.
Choose Target unit. The summary should show the selected target value, and the Target row in Target Conversion should match it.
Open Advanced if you need a different Display precision, Number notation, Pair curve range, or Unit list filter.
Check Base and Formula in Target Conversion. These rows explain the base reference and the conversion path used for the displayed target.
Open All Equivalent Units if the selected target is not the only useful label. The source and target rows are highlighted when they appear in the table.
Open Conversion Guidance if the Guardrail row or warning area asks for review. Correct the category, source value, or unit before using the result.
Open Pair Range Curve when you want a visual check around the current source value. The current source value is marked on the chart.

Interpreting Results:

The large summary value and the Target row are the selected conversion result. The unit symbol is part of the answer. Copying 465.6613 without GiB, or 9.4086 without L/100 km, leaves out the meaning.

Use the Base row as the main trust check. If 12 in shows 0.3048 m, the length conversion is using the expected reference. If a pressure, torque, or fuel-economy base value looks surprising, check the category and source unit before assuming the target number is wrong.

Unit converter result areas and how to verify them
Result area	What to trust	What not to overread
Target Conversion	The Target, Base, Formula, and Guardrail rows for the selected pair.	A rounded display is not proof that the source value was measured to that precision.
All Equivalent Units	Each row expresses the same source measurement in another supported unit.	The table is not a list of separate measurements.
Conversion Guidance	Category-specific notes and any input warning rows.	A warning is not just a display note; it may mean the physical quantity is impossible or questionable.
Pair Range Curve	The shape of the relationship around the chosen source value.	The chart is an inspection aid; use the table for the exact copied value.

A clean result does not prove the original measurement was correct. It only proves the entered number, category, source unit, and target unit produced a valid conversion. Keep the source label, converted value, and unit together when the result will be checked later.

Worked Examples:

Package dimension. Set Category to Length, enter 12 in Source measurement, choose inches, and target centimeters. The summary and Target row show 30.48 cm. The Base row shows 0.3048 m, and the Formula row gives the inch-to-centimeter factor path.

Storage label comparison. Set Category to Digital storage, enter 500, choose GB, and target GiB. The Target row shows about 465.6613 GiB at four decimals. The Base row shows bytes, and Conversion Guidance reminds you that GB uses powers of 1000 while GiB uses powers of 1024.

Fuel economy inversion. Set Category to Fuel economy, enter 25, choose mpg US, and target L/100 km. The Base row converts through km/L, while the Target row shows about 9.4086 L/100 km. A lower L/100 km number means less fuel consumed per distance, so it moves in the opposite direction from mpg.

Temperature boundary. Set Category to Temperature, enter 20, choose deg C, and target deg F. The Target row shows 68 deg F, and the Base row shows 293.15 K. If the source is -300 deg C, the warning states that the value is below absolute zero and the target result is not valid.

Troubleshooting a strange answer. If a floor note says 100 ft2 but Category is Length, the answer is a distance conversion. Change Category to Area, keep 100 as the source value, choose square feet, and target square meters. The Target row should then describe area rather than length.

FAQ:

Why does the category matter so much?

The category decides which units are compatible. Feet, square feet, and cubic feet are related by name, but they measure length, area, and volume. Choose the category that matches the source label before trusting the target result.

Why does temperature not use the same factor formula?

Celsius and Fahrenheit use different zero points, so they need offsets around kelvin. Values below 0 K are blocked because they do not describe a physical absolute temperature.

Why are GB and GiB different?

The Digital storage category treats GB as decimal gigabytes and GiB as binary gibibytes. GB uses powers of 1000, while GiB uses powers of 1024, so the same byte count displays as different numbers.

What should I do when a warning appears?

Read the warning before using the result. It may indicate blank input treated as zero, invalid input reset to a default value, a negative physical quantity, a non-positive fuel-economy value, or a temperature below absolute zero.

Does display precision change the math?

No. Display precision changes visible decimals in the summary, tables, chart data, and JSON display values. The conversion is calculated before the display value is rounded.

Does the conversion use a server calculation?

No server-side calculation is used for the measurement conversion. The browser builds the summary, result tables, chart data, copied text, and downloadable output from the current inputs.

Glossary:

Base reference: The category unit used as the middle step, such as meter for length, kelvin for temperature, or byte for digital storage.
Factor conversion: A conversion where the source value is multiplied or divided by fixed ratios.
Scale offset: A fixed shift between temperature scales, such as the offset between Celsius and kelvin.
Absolute zero: The lower bound of absolute temperature, equal to 0 K.
Binary prefix: A digital-unit prefix based on powers of 1024, such as KiB, MiB, and GiB.
Fuel consumption: A fuel-economy form such as L/100 km where lower values mean less fuel used per distance.
Pair Range Curve: A chart of source values and target values for the currently selected unit pair.

References:

NIST Guide to the SI, Appendix B: Conversion Factors, NIST.
SI Units - Temperature, NIST.
Metric (SI) Prefixes, NIST.
Definitions of the SI units: The binary prefixes, NIST.
Unified Code for Units of Measure, UCUM Organization and Regenstrief Institute.