True Airspeed Calculator

Plotly graph

The chart updates after you calculate.

Interactive • Zoom • Hover values

Tip: Use the mode bar to zoom, pan, and reset.

Calculator

Choose a method, enter values, then calculate.

White Theme • Responsive Form Grid

Method

Density method is common for flight planning.

Output speed unit

All displayed speeds follow this unit.

Outside air temperature

Used for density and speed of sound.

Airspeed value

Enter indicated, calibrated, or equivalent speed.

Airspeed type

This tool assumes IAS/CAS ≈ EAS.

Pressure altitude

Use pressure altitude, not field elevation.

Wind speed (optional)

Adds wind components and groundspeed.

Wind direction FROM (°)

Use degrees true where possible.

Aircraft heading (°)

Direction aircraft is going toward.

Mach number

TAS = Mach × speed of sound.

When to use Mach method

Use Mach when the aircraft is operating near cruise where Mach hold is relevant. Temperature strongly controls the speed of sound and thus TAS.

Reset

Example data table

These examples use the density method and treat CAS as EAS.

CAS (kt)	Pressure Altitude (ft)	OAT (°C)	Estimated TAS (kt)	Mach
120	8,000	5	136.8	0.210
150	12,000	-2	182.5	0.284
95	3,000	25	102.1	0.152

Formula used

Density method

TAS ≈ EAS / √(ρ / ρ₀)

This estimate uses density ratio σ = ρ/ρ₀. It is widely used for flight planning and performance checks.

Mach method

TAS = M × a, a = √(γRT)

The speed of sound depends on absolute temperature T. With γ≈1.4 and R≈287.05, the result is in m/s.

ρ is computed using ISA pressure at pressure altitude and measured OAT.
ρ₀ is sea-level standard density, about 1.225 kg/m³.
Mach is computed as TAS / a after unit conversion.
Density altitude is an approximation for quick operational insight.

How to use this calculator

Select the method: density-based is best for most GA scenarios.
Choose your output unit so all results match your preference.
Enter outside air temperature and, if needed, pressure altitude.
Enter airspeed, then add wind and heading if you want groundspeed.
Press Calculate and review TAS, Mach, and atmosphere details.
Use Download CSV or Download PDF for records.

Safety note: This tool provides engineering estimates and training-grade outputs. For certified performance planning, use approved aircraft documentation and avionics.

Measurement inputs and units

This calculator accepts indicated, calibrated, or equivalent airspeed with knots, mph, km/h, or m/s. Internally, speeds are converted using 1 kt = 0.514444 m/s and 1 mph = 0.44704 m/s. Pressure altitude can be entered in feet or meters, and temperature in °C or °F, then converted to Kelvin for thermodynamic equations.

Density ratio and true airspeed

True airspeed increases as air density decreases. The tool estimates density with ρ = P/(R·T), then uses σ = ρ/ρ0 with ρ0 = 1.225 kg/m³. A practical takeaway: if σ drops to 0.80, TAS rises by about 1/√0.80 ≈ 1.118, meaning roughly 12% higher than EAS at the same lift condition.

Pressure altitude and ISA pressure

Pressure altitude is used to obtain a standard-atmosphere static pressure P, keeping the model consistent with altimeter settings. Below 11 km, the ISA lapse rate is applied; above that, an isothermal layer is used. Using pressure altitude rather than field elevation reduces bias when QNH differs from 1013.25 hPa.

Mach and speed of sound

For high-altitude cruise, Mach is often the controlling variable. The calculator uses a = √(γRT) with γ ≈ 1.4 and R ≈ 287.05 J/(kg·K). At 15 °C, a is about 340 m/s, while at −30 °C it is about 303 m/s, so the same Mach yields lower TAS in colder air.

Wind components and groundspeed

When wind speed, wind-from direction, and aircraft heading are provided, the tool computes headwind and crosswind components with simple trigonometry. Groundspeed is approximated as GS ≈ TAS − headwind component. This supports quick route estimates, while still keeping the primary output focused on air-mass-relative speed.

Quality checks and reporting

Results include TAS, Mach, speed of sound, and key atmosphere values to help validate inputs. If values look unusual, verify that altitude is pressure altitude and temperature is outside air temperature, not ISA. CSV export supports audit trails, and the PDF snapshot is suitable for briefings, training notes, and engineering records.

Density altitude is also estimated for operational context: DA ≈ PA + 118.8 × (OAT − ISA_T) in feet. For example, at PA 8,000 ft and OAT 25 °C, DA is near 11,000 ft, signaling reduced climb and longer takeoff distance in hot conditions.

FAQs

What is true airspeed (TAS)?

TAS is the aircraft’s speed relative to the surrounding air mass. It differs from ground speed because wind can add or subtract from the air-mass motion along your track.

Which altitude should I enter?

Enter pressure altitude whenever possible. You can get it by setting 1013.25 hPa (29.92 inHg) on the altimeter and reading altitude, or by using your avionics’ pressure altitude field.

Why does TAS increase as you climb?

At a given lift condition, equivalent airspeed stays tied to dynamic pressure. As air density drops with altitude, you must move through a larger volume of air each second, so true airspeed rises.

Does IAS equal EAS in this calculator?

For practical estimates, the tool treats IAS and CAS as equivalent airspeed. At higher Mach or with large instrument/position errors, the difference can matter; use EAS if you have it for best accuracy.

How is Mach computed?

Mach is TAS divided by the local speed of sound. The speed of sound is calculated from temperature using a = √(γRT), so colder air reduces a and changes TAS for a given Mach.

Why might results differ from my aircraft computer?

Certified systems may apply compressibility corrections, sensor calibration curves, and refined atmospheric models. Differences also appear if you enter indicated altitude instead of pressure altitude, or if temperature is not true outside air temperature.