What does KIAS mean, and how do you convert it to mph, km/h, m/s, and true airspeed?
Learn what KIAS means, convert KIAS to mph, km/h and m/s, and calculate true airspeed correctly using altitude and temperature.
KIAS means knots indicated airspeed: the speed shown by an aircraft’s airspeed indicator, expressed in nautical miles per hour. To change only the units, multiply KIAS by 1.15078 for mph, 1.852 for km/h, or 0.514444 for m/s. Converting KIAS to true airspeed also requires altitude, temperature and aircraft correction data.
What exactly does KIAS mean?
KIAS stands for knots indicated airspeed, meaning the uncorrected airspeed displayed to the pilot. In real-world aviation and flight simulation, the indication comes from the pitot-static system’s pressure measurements rather than GPS movement over the ground.
One knot is one nautical mile per hour, and one nautical mile is exactly 1,852 metres. “Knots per hour” is incorrect because a knot is already a rate of speed.
KIAS is used for most cockpit handling targets, including take-off, climb and approach speeds, because it reflects the aerodynamic pressure acting on the aircraft. Check the aircraft documentation, though: performance data may specify KIAS, KCAS or another airspeed rather than using the terms interchangeably.
How do you convert KIAS to mph, km/h or m/s?
Converting KIAS into another unit is a direct multiplication, but the result remains indicated airspeed.
| Required unit | Conversion from KIAS | 100 KIAS equals |
|---|---|---|
| mph | KIAS × 1.150779 | 115.08 mph indicated |
| km/h | KIAS × 1.852 | 185.2 km/h indicated |
| m/s | KIAS × 0.514444 | 51.44 m/s indicated |
For the reverse conversion, divide mph by 1.150779, km/h by 1.852, or m/s by 0.514444. These calculations change only the unit: 100 KIAS becoming 115.08 mph does not make it true airspeed or groundspeed.
Can you convert KIAS directly to true airspeed?
KIAS cannot be converted accurately to true airspeed from the indicated number alone. You also need atmospheric conditions and, for precision, the aircraft’s airspeed correction data.
- Correct IAS to calibrated airspeed. Use the aircraft flight manual or pilot’s operating handbook to account for instrument and position error. The correction can vary with speed, flap setting and configuration.
- Correct for compressibility. Converting calibrated airspeed to equivalent airspeed matters most for faster aircraft and higher altitudes; the difference is usually small in a slow light aircraft.
- Correct for air density. Use pressure altitude and outside air temperature, or measured static pressure and temperature, to convert equivalent airspeed into true airspeed.
For low-speed estimates where KIAS is close to equivalent airspeed, the relationship is:
KTAS ≈ KIAS × √(ρ₀ ÷ ρ)
Here, ρ₀ is standard sea-level air density and ρ is the actual air density. A flight computer or avionics system normally performs this calculation from pressure altitude and outside air temperature.
A familiar shortcut adds roughly 2% to IAS for every 1,000 feet above sea level. It is only a rough lower-altitude estimate under near-standard conditions; temperature departures, compressibility and instrument error can make it inaccurate. Once KTAS is known, the same unit factors above convert it to true mph, km/h or m/s.
Why are KIAS, KTAS and groundspeed different?
KIAS, KTAS and groundspeed measure different things, so disagreement between them is normal.
- KIAS: the cockpit airspeed indication, used for most handling and operational speed targets.
- KTAS: the aircraft’s actual speed through the surrounding air mass, expressed in knots.
- Groundspeed: movement over the Earth’s surface; wind changes it relative to true airspeed.
At altitude, thinner air means the aircraft must move faster through the air to produce the same indicated pressure, so KTAS is normally higher than KIAS. A headwind then makes groundspeed lower than KTAS, while a tailwind makes it higher. Our explanation of how IAS, true airspeed and Mach behave with altitude covers this relationship in more detail.
Why does a flight simulator show several different speeds?
A simulator may display IAS on the cockpit airspeed tape while a GPS, navigation display or external overlay shows TAS or groundspeed. Before treating different numbers as an error, check whether each value is labelled IAS, CAS, TAS, GS or Mach.
Weather settings also matter. Changes in altitude, pressure, temperature and wind can separate KIAS, KTAS and groundspeed substantially even when the simulated aircraft is holding a steady indicated speed. If the instruments themselves are unclear, our guide to identifying and reading the main MSFS flight instruments explains where indicated airspeed fits among the other cockpit indications.