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Includes everyday, engineering, astronomical, digital, and fuel-economy quantities.
The conversion updates immediately; changing units preserves the entered digits because this tool converts the stated source measurement.
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Formatting never changes the underlying converted value.
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Fuel Efficiency Converter Convert MPG (US), L/100 km, and km/L with reciprocal formulas, clear direction guidance, and warnings for unusual or mistyped readings.
Data Transfer Rate Converter Convert data transfer rates across bit and byte units in SI or IEC notation, with overhead modeling, payload timing and delivery-window capacity.
File and Disk Size Converter Convert file and disk sizes between decimal and IEC units, then estimate usable capacity and allocation slack for storage planning.
Shoe Size Converter Convert foot length or a regional shoe label into cross-system sizes with adjustable allowance, retail rounding, and fit-drift guidance.

A measurement carries both a number and a unit. Removing the unit turns 60 mph, 60 km/h, and 60 m/s into the same-looking number even though they describe very different speeds. Reliable conversion preserves the physical quantity while changing the scale used to express it.

Most units convert through a common reference unit. Length can pass through meters, pressure through pascals, energy through joules, and digital storage through bytes. A source factor places the quantity on that common scale; a target factor then expresses it in the requested unit.

Conversion issueWhy it mattersExample
Offset scalesThe zero points differ, so a factor alone is wrong.Celsius and Fahrenheit
Inverse measuresA better efficiency produces a smaller consumption number.mpg and L/100 km
Squared or cubed unitsThe length relationship is raised to the second or third power.ft² to m² or ft³ to L
Decimal and binary prefixesPowers of 1000 and 1024 produce different storage values.GB and GiB
Calendar averagesA fixed average cannot reproduce a specific calendar interval.Months and years as durations

Unit choice also carries context. A US gallon differs from an imperial gallon; a nautical mile is fixed at 1852 meters; mechanical and metric horsepower are not identical. The source's region, discipline, and written symbol matter as much as the digits.

Precision should follow the measurement, not the length of the converted number. Extra decimal places do not recover uncertainty lost in the original reading. For construction, laboratory, finance, or safety work, keep the original value and use the tolerance and rounding rules required by the governing standard.

Conversion compares equivalent quantities. It does not decide whether the original measurement is accurate, whether two instruments are calibrated alike, or whether a rounded result is suitable for a regulated calculation.

How to Use This Tool:

Choose the kind of quantity before selecting units; units from different categories cannot describe the same measurement.

  1. Select Category, then enter the Source measurement with its actual source unit.
  2. Choose the Target unit. Check regional variants such as US and imperial gallons before accepting the result.
  3. Set Display precision and Number notation for the destination document. These choices format the result without changing the underlying converted value.
  4. Review Conversion audit for the base value and formula. Use All units when a second equivalent helps catch a category or prefix mistake.

Interpreting Results:

The headline value is an equivalent quantity in the selected target unit. The base value is the best audit point when several units are being compared because every equivalent in the category comes from that same quantity.

  • Scientific and engineering notation change presentation only. Engineering exponents move in multiples of three.
  • A displayed result is rounded to 2, 4, 6, or 8 decimal places, while conversion calculations retain full numeric precision.
  • Fuel-consumption units run in the opposite direction from fuel-efficiency units. A lower L/100 km value indicates better economy, while a higher mpg value indicates better economy.

Technical Details:

The 21 measurement categories use category-specific reference units. Linear categories multiply into the reference unit and divide out to the target. Temperature adds scale offsets, while fuel economy may invert a consumption value.

Formula Core:

For linear categories, one pair of factors is enough.

B=Vs×Fs Vt=BFt

Vs and Vt are the source and target values, Fs and Ft are their reference-unit factors, and B is the category's base value.

Temperature passes through kelvin. Celsius, Fahrenheit, and Rankine therefore use both offsets and scale ratios.

K=VC+273.15 K=(VF+459.67)×59

Fuel economy passes through kilometers per liter. Consumption units use the reciprocal relationship.

E=100C×F

E is kilometers per liter, C is a consumption value such as L/100 km or US gal/100 mi, and F converts that consumption unit to the L/100 km basis.

Category groupReference units
Distance and geometryLength: m; astronomical distance: km; area: m²; volume: L
Motion and flowVolume flow: m³/s; speed: m/s; acceleration: m/s²
Mechanical quantitiesMass: kg; force: N; torque: N m; pressure: Pa; density: kg/m³
Energy and cyclesEnergy: J; power: W; frequency: Hz; angle: rad; time: s
Special scalesTemperature: K; fuel economy: km/L
Digital quantitiesStorage: B; data rate: bit/s

Rule Core:

  • The source must be a finite number.
  • Temperature is rejected when its kelvin equivalent is below 0 K.
  • Fuel-economy and fuel-consumption inputs must be greater than zero because reciprocal conversion is undefined at zero.
  • Equivalent-unit and pair-range values come from the same unrounded base value as the headline result.

Accuracy Notes:

Definitions and exact factors do not remove uncertainty from the source measurement.

  • Choose the explicit US or imperial gallon variant rather than assuming that mpg has one universal meaning.
  • Average month and year durations use a 365.2425-day Gregorian average; use calendar date arithmetic for a specific interval.
  • Decimal storage prefixes use powers of 1000 and IEC binary prefixes use powers of 1024.
  • Round at the final reporting stage unless the governing procedure requires a different rule.

Worked Examples:

Room area

A 100 ft² room uses the exact factor 0.09290304 m² per ft², producing 9.290304 m² before display rounding. Selecting four decimal places shows 9.2903 m² without changing the underlying value.

Temperature with an offset

For 20 °C, kelvin is 293.15 K. Converting that base value to Fahrenheit gives 68 °F. Multiplying 20 by 9/5 without adding 32 would be wrong because the scales have different zero points.

Fuel efficiency and consumption

A rating of 25 mpg US converts to about 10.628593 km/L, then inverts to about 9.408583 L/100 km. The lower consumption number describes the same vehicle efficiency.

References: