True Airspeed Calculator

Convert indicated airspeed to true airspeed using altitude and temperature corrections.

Calculate the actual speed of an aircraft through the air by accounting for air density changes with altitude and temperature.

Examples

Click on any example to load it into the calculator.

Commercial Aircraft Cruise

Commercial Aviation

Typical cruise conditions for a commercial airliner at high altitude.

IAS: 250 knots

Altitude: 35000 ft

Temperature: -45 °C

General Aviation Flight

General Aviation

Common conditions for a small aircraft flying at moderate altitude.

IAS: 120 knots

Altitude: 8000 ft

Temperature: 10 °C

Flight Training

Flight Training

Typical conditions for student pilot training flights.

IAS: 80 knots

Altitude: 3000 ft

Temperature: 20 °C

Mountain Flying

Mountain Flying

High-altitude conditions for mountain flying operations.

IAS: 140 knots

Altitude: 12000 ft

Temperature: 5 °C

Pressure Alt: 12500 ft

Other Titles
Understanding True Airspeed Calculator: A Comprehensive Guide
Master the essential aviation calculation that converts indicated airspeed to true airspeed, accounting for the effects of altitude and temperature on air density.

What is True Airspeed?

  • Definition and Importance
  • IAS vs TAS
  • Why It Matters for Pilots
True Airspeed (TAS) is the actual speed of an aircraft relative to the air mass through which it is flying. Unlike Indicated Airspeed (IAS), which is what the pilot reads on the airspeed indicator, TAS accounts for the effects of altitude and temperature on air density. This is crucial for accurate flight planning, fuel calculations, and navigation.
The Difference Between IAS and TAS
Indicated Airspeed (IAS) is the speed shown on the aircraft's airspeed indicator, measured by the pitot-static system. It represents the dynamic pressure of the air hitting the aircraft. However, as altitude increases, air density decreases, so the same IAS at higher altitudes actually represents a higher true speed through the air. TAS is always equal to or greater than IAS, with the difference becoming more pronounced at higher altitudes.
Why True Airspeed is Critical
TAS is essential for accurate flight planning, fuel consumption calculations, and navigation. Ground speed (the speed over the ground) is calculated by combining TAS with wind components. Without knowing TAS, pilots cannot accurately determine flight times, fuel requirements, or navigate effectively, especially on long flights or at high altitudes.
Real-World Impact
At sea level, IAS and TAS are nearly identical. But at 35,000 feet, an aircraft showing 250 knots IAS might actually be flying at 450 knots TAS. This dramatic difference affects everything from fuel planning to arrival times and is why TAS calculations are mandatory for commercial aviation.

Key Aviation Speed Terms:

  • Indicated Airspeed (IAS): Speed shown on the airspeed indicator
  • True Airspeed (TAS): Actual speed through the air mass
  • Ground Speed (GS): Speed over the ground (TAS ± wind)
  • Calibrated Airspeed (CAS): IAS corrected for instrument errors

Step-by-Step Guide to Using the Calculator

  • Gathering Required Data
  • Inputting Values
  • Interpreting Results
Using the True Airspeed Calculator requires accurate input data to produce reliable results. Follow these steps to ensure accurate calculations.
1. Obtain Indicated Airspeed
Read the IAS directly from your aircraft's airspeed indicator. This is typically displayed in knots for most aircraft. Ensure the instrument is properly calibrated and functioning correctly. For training purposes, you can use typical values: 80-120 knots for small aircraft, 200-300 knots for commercial aircraft.
2. Determine Current Altitude
Use your altimeter to read the current altitude above sea level. Most altimeters display altitude in feet. For the most accurate TAS calculation, use pressure altitude if available, as it accounts for non-standard atmospheric pressure conditions.
3. Measure Outside Air Temperature
Read the outside air temperature (OAT) from your aircraft's temperature gauge. This is typically displayed in degrees Celsius. Temperature significantly affects air density and therefore TAS calculations. Warmer air is less dense, resulting in higher TAS for the same IAS.
4. Enter Data and Calculate
Input all values into the calculator, ensuring units are correct (knots for speed, feet for altitude, Celsius for temperature). The calculator will automatically apply the necessary corrections and display your true airspeed along with related atmospheric data.

Typical Input Values by Aircraft Type:

  • Small Aircraft: IAS 100 knots, Altitude 3,000 ft, Temp 15°C
  • Commercial Aircraft: IAS 250 knots, Altitude 35,000 ft, Temp -45°C
  • Military Aircraft: IAS 400 knots, Altitude 25,000 ft, Temp -30°C
  • Helicopter: IAS 80 knots, Altitude 1,500 ft, Temp 20°C

Real-World Applications and Aviation Scenarios

  • Flight Planning
  • Fuel Management
  • Navigation
True airspeed calculations are fundamental to safe and efficient aviation operations across all sectors of the industry.
Commercial Aviation Operations
Commercial pilots use TAS for precise flight planning, fuel calculations, and scheduling. At high altitudes, the difference between IAS and TAS can be substantial, directly impacting fuel consumption and flight duration. Airlines rely on accurate TAS calculations to optimize routes, reduce costs, and maintain schedules.
General Aviation and Training
Student pilots learn TAS calculations as part of their basic training. Understanding the relationship between IAS and TAS is crucial for safe cross-country flights, especially when flying at different altitudes or in varying weather conditions. Private pilots use TAS for accurate navigation and fuel planning.
Military and Specialized Operations
Military pilots require precise TAS calculations for mission planning, weapon delivery, and formation flying. High-performance aircraft operating at various altitudes and speeds depend on accurate TAS for tactical operations and safety.

Common Misconceptions and Aviation Myths

  • Speed vs. Ground Speed
  • Altitude Effects
  • Temperature Impact
Several misconceptions exist about airspeed and its relationship to aircraft performance and navigation.
Myth: IAS is Always the Same as TAS
This is perhaps the most common misconception. IAS and TAS are only equal at sea level under standard atmospheric conditions. As altitude increases, air density decreases, causing the same IAS to represent a higher TAS. At 35,000 feet, TAS can be nearly double the IAS.
Myth: Higher Altitude Always Means Higher TAS
While TAS generally increases with altitude for the same IAS, this relationship depends on maintaining the same IAS. If a pilot reduces IAS as they climb (which is common for fuel efficiency), TAS might actually decrease. The key is understanding the relationship between IAS, altitude, and air density.
Myth: Temperature Doesn't Significantly Affect TAS
Temperature has a significant impact on air density and therefore TAS. Hot air is less dense than cold air, so the same IAS in hot conditions results in a higher TAS. This is why pilots must consider temperature in their calculations, especially in extreme weather conditions.

Expert Tip:

  • Always verify your TAS calculations with your aircraft's performance charts and consider using multiple methods to cross-check your results for critical flights.

Mathematical Derivation and Formulas

  • Air Density Calculations
  • TAS Formula
  • Standard Atmosphere
The calculation of true airspeed involves understanding air density and its relationship to atmospheric conditions. The mathematical foundation is based on the International Standard Atmosphere (ISA) model and gas laws.
The True Airspeed Formula
The basic formula for calculating TAS from IAS is: TAS = IAS × √(ρ₀/ρ), where ρ₀ is the air density at sea level under standard conditions (1.225 kg/m³) and ρ is the actual air density at the current altitude and temperature. This formula accounts for the relationship between dynamic pressure and air density.
Air Density Calculations
Air density is calculated using the ideal gas law: ρ = P/(R×T), where P is atmospheric pressure, R is the specific gas constant for air (287 J/kg·K), and T is absolute temperature in Kelvin. Pressure decreases exponentially with altitude according to the barometric formula, while temperature varies with altitude in the standard atmosphere.
Standard Atmosphere Model
The International Standard Atmosphere (ISA) defines standard conditions: sea level pressure of 1013.25 hPa, temperature of 15°C, and a temperature lapse rate of 6.5°C per 1000 meters. Deviations from these standard conditions require corrections using pressure altitude and temperature deviation calculations.

Important Atmospheric Constants:

  • Standard Sea Level Pressure: 1013.25 hPa (29.92 inHg)
  • Standard Sea Level Temperature: 15°C (59°F)
  • Temperature Lapse Rate: 6.5°C per 1000m (2°C per 1000ft)
  • Gas Constant for Air: 287 J/kg·K