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American pilots mix several measurement systems: knots and nautical miles for navigation, statute miles for some visibility, inches of mercury for altimeter settings and US gallons or pounds for fuel. The habit that prevents most mistakes is to name both the number and what it is measured against before you use it.
Checked against: Conversion factors are standard mathematical constants; terminology checked against the FAA Pilot/Controller Glossary and FAA Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25), as summarized in Aero Academic’s 27 October 2026 editorial brief; flight instructor review pending before publication.
| Term | Meaning |
|---|---|
| FAA | Federal Aviation Administration, the authority responsible for pilot certification |
| AME | Aviation Medical Examiner in the FAA medical process |
| MedXPress | The FAA’s online medical application system |
| IACRA | Integrated Airman Certification and Rating Application |
| FTSP | Flight Training Security Program, run by the TSA |
| ACS | Airman Certification Standards, listing what you must know and do for a certificate |
| PIC | Pilot in command, the pilot responsible for the safe conduct of the flight |
| Solo | In the ordinary student airplane or helicopter context, flight with the student as the sole occupant |
| VFR | Visual Flight Rules |
| AIM | Aeronautical Information Manual |
| Term | What it refers to |
|---|---|
| METAR | A routine aviation weather report |
| TAF | A terminal forecast for an airport |
| MSL | Mean sea level, the reference for altitude |
| AGL | Above ground level, the reference for height above the terrain |
| Altimeter setting | The pressure setting that makes an altimeter read altitude, given in inches of mercury (for example 29.92 inHg) |
| Flight level (FL) | A pressure-based level referenced to 29.92 inches of mercury; in the United States it applies at and above 18,000 feet MSL |
| UTC | Coordinated Universal Time, also called Zulu, used on weather reports |
| Density altitude | Pressure altitude corrected for nonstandard temperature, a measure of how the aircraft will perform |
| Convert | Calculation |
|---|---|
| Nautical miles to statute miles | Multiply by approximately 1.15078 |
| Statute miles to nautical miles | Divide by approximately 1.15078 |
| Nautical miles to kilometers | Multiply by 1.852 |
| Knots to miles per hour | Multiply by approximately 1.15078 |
| Knots to kilometers per hour | Multiply by 1.852 |
| Feet to meters | Multiply by 0.3048 |
| Pounds to kilograms | Multiply by 0.45359237 |
| US gallons to liters | Multiply by 3.785411784 |
| Imperial gallons to liters | Multiply by 4.54609 |
| Minutes to decimal hours | Divide by 60 |
| Decimal hours to minutes | Multiply by 60 |
Aviation language is dense with abbreviations, and a student in the United States works with several measurement systems at once. Navigation uses nautical miles and knots. Visibility in reports is given in statute miles. Altimeter settings use inches of mercury. Fuel is measured in US gallons and aircraft weights in pounds. None of that is hard, but mixing them up is the commonest arithmetic mistake a beginner makes.
The cure is a habit. Every time you meet a number, say what it measures and what it is measured from. Is the distance nautical or statute? Is the height above ground level or above mean sea level? Is the speed through the air or over the ground? A number without its reference is only half an answer.
Worked examples in this guide are hypothetical, and they are labeled that way so that nobody mistakes them for aircraft data. For real flights always use the approved documents for your aircraft.
Table 1 collects the terms you will hear in your first weeks. The FAA medical, IACRA and TSA process is explained in our paperwork guide, and the ACS is explained in our ACS guide.
A regional warning: do not assume an abbreviation means the same thing in the United States and Australia. Terms like PPL, ARN, DAME and ASIC are Australian, while IACRA, AME and MedXPress are American. The two countries use different words for the same idea, so check which country a source is talking about before you use a term in your own notes.
Table 2 lists the weather and altitude terms. MSL and AGL are the two references you will use most. An altitude is measured above mean sea level, and a height is measured above the ground, so a 2,000-foot AGL cloud base over a 1,000-foot hill is at a different altitude from the same base over flat ground.
The altimeter setting is given in inches of mercury in the United States. The standard setting is 29.92 inHg, and a flight level is a pressure-based level referenced to it. In the United States flight levels apply at and above 18,000 feet MSL, which is well above where most student flying happens.
Do not use altitude, height and flight level as if they were the same word. They can differ by hundreds of feet.
Time on weather reports is in UTC, which pilots also call Zulu. Convert it to local time before you decide whether a forecast applies to your flight.
Table 3 gives the conversions you will use most. They are mathematical constants, not aircraft performance data. A knot is one nautical mile per hour, and a nautical mile is exactly 1.852 kilometers, which is about 1.15078 statute miles. Never use a statute mile when you are working with nautical distances.
Write the units beside every number as you calculate, and cross them out as they cancel. It feels slow for the first week and then it saves you.
For an authoritative definition of a term, use the FAA Pilot/Controller Glossary and the Aeronautical Information Manual rather than a forum.
Example (hypothetical): convert 25 nautical miles to statute miles. 25 × 1.15078 = 28.77, so 25 NM is about 28.8 statute miles.
Example (hypothetical): convert 100 knots to miles per hour. 100 × 1.15078 = 115.08, so 100 knots is about 115.1 mph.
Example (hypothetical): convert 2,000 feet to meters. 2,000 × 0.3048 = 609.6, so 2,000 feet is 609.6 meters. These are unit conversions only. They do not change the units that an aircraft limitation, a chart or a clearance requires.
Writing just “gallons” is ambiguous, because a US gallon and an Imperial gallon are different sizes. Twenty US gallons is 20 × 3.785411784 = 75.70823568, or 75.71 liters to two decimal places. Twenty Imperial gallons is 20 × 4.54609 = 90.9218, or 90.92 liters. The difference is 15.21 liters.
In the United States, fuel is normally sold and recorded in US gallons. If you read a manual written for another country, check whether it uses Imperial gallons or liters, because quoting the wrong one gives a fuel error of about a fifth.
Fuel also has weight. Mass equals volume multiplied by density, and the FAA handbooks commonly use a round figure for aviation gasoline of about 6 pounds per US gallon. Use the figure in your aircraft’s own documentation, and remember that other fuels have different densities.
Decimal hours are not clock notation. To convert 1 hour 30 minutes, add 30 ÷ 60 = 0.5 to the 1 hour, which gives 1.5 hours. To go the other way, 1.3 hours is 1 hour plus 0.3 × 60 = 18 minutes, so 1 hour 18 minutes, not 1 hour 30 minutes.
Learn this before you start using hourly fuel burn figures or logging decimal flight time, because your logbook and your fuel plan both depend on it.
Distance equals speed multiplied by time, with compatible units. Using knots and hours gives nautical miles. Rearranged, time in hours equals distance in nautical miles divided by groundspeed in knots.
Example (hypothetical): a leg is 60 NM and the planned groundspeed is 90 knots. 60 ÷ 90 = 2/3 hour, and 2/3 × 60 = 40 minutes. Use groundspeed, not airspeed, for this calculation.
Example (hypothetical): assume a constant fuel flow of 6 US gallons per hour for that 40-minute leg. 6 × 40/60 = 4, so the simplified segment uses 4 US gallons. That is not a complete fuel plan. It leaves out other phases of flight, contingencies, and the reserve required by the rules for your operation.
Before you accept an answer, ask the same short list of questions. What quantity is being calculated? Which units are the inputs using? Are any conversions needed? Which reference applies, MSL or AGL, nautical or statute? Is the result rounded sensibly? Does it make practical sense? Which approved document governs the real operation?
Pilots who ask those questions routinely catch errors before they matter. When you are ready to practice, use the free E6B flight computer on this site, and check your answers against the factors in Table 3.
A nautical mile is exactly 1.852 kilometers, about 1.15078 statute miles. Aviation navigation uses nautical miles and knots, while some visibility in reports uses statute miles. Do not substitute one for the other when you work with distances.
The US altimeter setting is given in inches of mercury, and the standard setting is 29.92 inHg. A flight level is referenced to that standard pressure and applies at and above 18,000 feet MSL in the United States.
Multiply the decimal part by 60. For example, 1.3 hours is 1 hour plus 0.3 × 60 = 18 minutes, so 1 hour 18 minutes. Decimal hours are not clock notation, and 1.3 does not mean 1 hour 30 minutes.
No. One US gallon is 3.785411784 liters and one Imperial gallon is 4.54609 liters, so twenty of each differ by about 15.21 liters. Always state which you mean, and check manuals written for other countries.
MSL means mean sea level and is the reference for altitude. AGL means above ground level and is the reference for height above the terrain. An altitude and a height are different measures, so always check which reference a number uses.
https://www.aeroacademic.com/guides/us-aviation-terms-units-conversions