Convert between the units aerospace engineers and pilots use every day — airspeed in m/s, km/h, knots, mph, and ft/s; altitude in m, km, feet, and nautical miles; pressure in Pa, kPa, hPa, psi, inHg, and atm; and thrust or force in N, kN, lbf, and kgf. Pick a category, enter a value, and choose your from and to units.
Aerospace is one of the few engineering fields where SI and US-customary units coexist in everyday use, and where mixing them up has caused real accidents. Airspeed is quoted in knots, altitude in feet, pressure in inches of mercury or hectopascals, and thrust in pounds-force or kilonewtons depending on whom you ask. This converter handles the four most common aerospace categories — airspeed, altitude, pressure, and thrust/force — by routing every value through its SI base unit.
Each unit is defined by how many SI base units it equals: for airspeed the base is m/s, for altitude it is metres, for pressure pascals, and for force newtons. To convert, the calculator first multiplies your value by the "from" factor to reach the base unit, then divides by the "to" factor:
result = value · factor[from] / factor[to]
This two-step base-unit approach means any unit in a category can convert to any other, and adding a new unit only needs its single base-unit factor. The SI base value is shown separately so you always see the underlying physical quantity.
Pilots almost universally use the knot — one nautical mile per hour, or 0.514444 m/s — for airspeed and groundspeed, because a nautical mile equals one minute of latitude and makes navigation arithmetic clean. Altitude in cruise is expressed as a flight level: FL350 means 35,000 feet of pressure altitude referenced to the standard 1013.25 hPa setting. Because one foot is exactly 0.3048 m, FL350 is about 10,668 m. Converting fluently between feet, metres, knots, and m/s is a daily necessity when mixing engineering analysis (SI) with operational data (customary).
Two famous failures show the cost of unit errors. In 1983 the Gimli Glider — a Boeing 767 — ran out of fuel mid-flight after ground crews loaded it using pounds where the new metric aircraft needed kilograms, leaving it with roughly half the fuel intended; the crew glided it to a safe landing. In 1999 NASA's Mars Climate Orbiter was lost because one team supplied thruster impulse in pound-force-seconds while the navigation software expected newton-seconds, putting the spacecraft on a fatally low trajectory. Both were pure unit-conversion mistakes, and both are why aerospace teams insist on explicit, checked unit handling.
Speed in aerospace is often quoted as a Mach number — the ratio of true airspeed to the local speed of sound. Because Mach is dimensionless, it is not in this converter: the same true airspeed corresponds to different Mach numbers depending on temperature and altitude, since the speed of sound falls with temperature. To work with Mach, convert your true airspeed to m/s here, then divide by the local speed of sound (about 340 m/s at sea level, around 295 m/s in the high troposphere) from the ISA model.
Routing through a single base unit per category keeps the conversion logic simple and accurate: each unit needs just one defining factor, and any pair of units converts with value·factor[from]/factor[to]. It also avoids accumulating rounding error from chaining intermediate conversions, and it makes the underlying physical quantity (in SI) visible.
A knot is one nautical mile per hour (1.852 km/h, 0.514444 m/s) and is based on a minute of latitude, which is why aviation and marine navigation use it. A statute mile per hour (mph) is 1.609 km/h, or 0.44704 m/s. A knot is about 15% faster than an mph, so confusing the two materially changes a speed.
They are different. One standard atmosphere (atm) is 101,325 Pa exactly. A hectopascal (hPa) is 100 Pa and is identical to the millibar; standard sea-level pressure is 1013.25 hPa. Aviation weather (METARs) often uses hPa or inches of mercury (inHg, 3386.39 Pa), so converting between them is routine for flight planning.
Units are category-specific — knots belong to airspeed, feet to altitude. When you switch category the previous unit keys no longer exist, so the converter resets the from and to selectors to valid units in the new category to keep the conversion well-defined.
Kilogram-force (kgf) is the force exerted by one kilogram under standard gravity, equal to 9.80665 N. Some engine specifications, particularly older or non-US ones, quote thrust in kgf (or "kp"). It is a force, not a mass — converting it to newtons or pounds-force (lbf, 4.44822 N) lets you compare engines on a consistent basis.