Aviation unit converter
Aviation runs on a mixture of units that no other field would tolerate: feet for altitude, nautical miles for distance, knots for speed, and a choice of two pressure units depending on where you are. This converts between them.
Calculator
What the result means
Pick a group, enter a value, and choose the units. Every unit in the group is shown converted at the same time, so you can read across rather than running the conversion again.
The groups are deliberately limited to units that appear in real aviation use. There is no point offering furlongs.
When this is useful
- Reading a chart, manual or report that uses different units from the ones you think in.
- Working between hectopascals and inches of mercury, which is the commonest conversion for anyone flying between Europe and North America.
- Converting a fuel quantity between litres and gallons, remembering that US and imperial gallons are different sizes.
How it is calculated
Each group has a base unit, and every other unit is defined by its exact conversion factor to that base. Values are converted into the base unit and back out, which avoids the rounding that creeps in when conversions are chained.
Temperature is handled separately because the scales have different zero points, so a conversion needs an offset as well as a factor.
value in base units, then out to the target unit, using exact defined factors
Worked example
- Group
- Distance
- Value
- 100 NM
- Convert to
- km
100 nautical miles is 185.2 kilometres.
Check: A nautical mile is defined as exactly 1,852 metres, so 100 of them is exactly 185,200 metres, which is 185.2 km. This one is exact by definition rather than approximate.
Limitations
- A hectopascal and a millibar are identical in size, so no conversion between them is offered or needed.
- Temperature differences do not convert the same way as temperatures. A rise of 10 C is a rise of 18 F, not 50 F.
- The converter works to a fixed number of decimal places per group, which is well beyond the precision any of these numbers deserve in practice.
Common mistakes
- Confusing nautical miles with statute miles. A nautical mile is about 15 percent longer, and a speed in mph is not a speed in knots.
- Confusing US gallons with imperial gallons. The imperial gallon is about 20 percent larger.
- Converting a temperature difference as though it were a temperature.
Sources
- Annex 5: Units of Measurement to be Used in Air and Ground Operations , SKYbrary, EUROCONTROL
- The International System of Units (SI) , Bureau International des Poids et Mesures