Educational calculators only. Not for operational flight planning.

Aviation Unit Conversion Calculator

Aviation mixes unit systems more than most fields: speeds in knots, altitudes in feet, visibility in statute miles or meters, pressure in inches of mercury or hectopascals, fuel in gallons, liters, pounds or kilograms. This converter takes one value in one unit and shows it in every other unit of the same kind.

It covers six groups: speed, distance and altitude, mass, volume, pressure and temperature. That is enough to follow a manual written in one system while reading weather and charts in another, or to check a conversion you did by hand. Each group is converted through an SI unit using exact definitions where they exist.

Inputs

Results

Enter your values and select Calculate.

Educational use only. Results are not certified for operational flight planning or aircraft performance decisions. Always use approved aircraft documentation and official aviation information before flight.

How to use this calculator

  1. Enter the number in Value.
  2. Open Unit and choose the unit that value is in. The list is grouped into Speed, Distance and altitude, Mass, Volume, Pressure and Temperature.
  3. Read the results: one row for each of the other units in that group.

Unit is the unit you are converting from; there is no target to choose because all the others are shown. Negative numbers are accepted only for distance and altitude, and for temperatures that stay above absolute zero, so a rate of descent has to be entered as a positive number. US gallons and imperial gallons are separate entries in the Volume group: check which one your source means before choosing.

Formula

value in SI = value × factor of the starting unit

result = value in SI ÷ factor of the target unit

temperature: K = °C + 273.15 and °C = (°F − 32) × 5 ÷ 9

What the variables mean

factor
the exact or conventional SI value of one unit, for example 1 kt = 1 852 ÷ 3 600 m/s
SI
the International System of Units

Worked example

These example values are illustrative round numbers, not data for any particular aircraft. Select "Fill in the example" in the calculator to load them.

Inputs

  • Value: 120
  • Unit: knots (kt)

Working

  1. Multiply by the factor of the starting unit (0.5144444444): 61.7333333 in the reference unit for this quantity.
  2. Divide by the factor of each target unit to get the results shown.

Result

  • Kilometers per hour: 222.24 km/h
  • Miles per hour: 138.0935 mph
  • Meters per second: 61.73333 m/s
  • Feet per minute: 12,152.23 ft/min
  • Feet per second: 202.5372 ft/s

Reading the result

Each row is labeled with the full name of a unit and gives the value to seven significant figures; the unit you started from is left out. For illustration, 120 kt returns 222.24 km/h, 138.0935 mph, 61.73333 m/s, 12,152.23 ft/min and 202.5372 ft/s. Rows never cross groups, so gallons become liters but never pounds or kilograms. A temperature is converted as a reading on a scale, which is the right treatment for an outside air temperature and the wrong one for a temperature difference.

Assumptions and limitations

  • The nautical mile, foot, statute mile, pound, US gallon and imperial gallon use their exact international definitions.
  • Inches and millimeters of mercury are converted with fixed conventional factors, not from the density of mercury at a particular temperature.
  • Mass and volume are separate groups and no fuel density is assumed, so a volume of fuel cannot be turned into a mass here.
  • Temperatures are treated as points on a scale with their offsets, not as intervals.
  • Results are rounded for display to seven significant figures, which is far finer than most aviation inputs are known.

Common mistakes

  • Converting a temperature difference with the scale formula: a reading of 10 °C is 50 °F, but a 10 °C rise is an 18 °F rise.
  • Mixing US and imperial gallons, when the imperial gallon is about 20% larger.
  • Reading the mph scale of an airspeed indicator as knots, or the reverse.
  • Confusing feet per minute with feet per second for vertical speed, a factor of 60.
  • Typing an altimeter setting in inches of mercury while hectopascals is selected, or the other way round.
  • Expecting gallons or liters of fuel to convert straight to pounds or kilograms without the density of that fuel at its temperature.

References

  1. National Institute of Standards and Technology, Guide for the Use of the International System of Units (SI), Special Publication 811.
  2. Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25).

These public sources explain the formulas and definitions used here. Citing them does not mean they have reviewed, endorsed or certified AviationCalc.

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