Indicated Airspeed to Ground Speed Calculator

Turn indicated airspeed into realistic trip planning numbers. Include altitude, temperature, pressure, and wind corrections. Compare TAS, heading, and ground speed with exportable summaries.

Calculator Inputs

Indicated airspeed (kt)

Instrument / position correction (kt)

Pressure altitude (ft)

Outside air temperature (°C)

Desired true course (°)

Wind direction from (°)

Wind speed (kt)

Route distance (nm)

Reset

Example Data Table

Scenario	IAS (kt)	Altitude (ft)	OAT (°C)	Course (°)	Wind From / Speed	TAS (kt)	GS (kt)	Time
Training hop	105	2500	18	90	150 / 12	113.3	106.8	00:34
Cross-country leg	128	6500	10	135	250 / 22	149.4	157.3	00:55
High-altitude cruise	145	9500	2	40	320 / 28	174.6	167.5	01:19

Formula Used

1. Calibrated airspeed: CAS = IAS + correction

2. ISA temperature: ISA Temp = 15 − 1.98 × altitude in thousands of feet

3. Density altitude: Density Altitude = Pressure Altitude + 120 × (OAT − ISA Temp)

4. True airspeed estimate: TAS ≈ CAS × [1 + 0.02 × (Density Altitude / 1000)]

5. Wind correction angle: WCA = asin(Crosswind ÷ TAS)

6. Ground speed: GS = TAS × cos(WCA) − Headwind

These formulas are practical planning approximations. They are useful for training, trip estimates, and quick comparisons, but they do not replace certified aircraft performance data or approved flight planning tools.

How to Use This Calculator

Enter indicated airspeed from the cockpit display in knots.
Add any correction that turns indicated airspeed into calibrated airspeed.
Enter pressure altitude and outside air temperature.
Provide desired course, wind direction from, and wind speed.
Add route distance to estimate time en route.
Press calculate to show the result above the form.
Use the CSV or PDF buttons to export the summary.

FAQs

1. What is the difference between IAS, TAS, and ground speed?

IAS is what the instrument shows. TAS adjusts that speed for air density. Ground speed is your actual movement over Earth after wind changes the aircraft’s path and progress.

2. Why do temperature and altitude matter?

As altitude or temperature changes, air density changes. Lower density means the aircraft moves through the air faster than the indicated reading suggests, so true airspeed usually increases.

3. How does wind direction change the answer?

A headwind reduces ground speed, a tailwind increases it, and a crosswind changes the heading required to stay on course. This calculator accounts for all three effects.

4. Why is heading different from course?

Course is the path you want over the ground. Heading is where the nose must point. Crosswind usually makes heading different from course because you must crab into the wind.

5. Can this replace aircraft manuals or approved flight planning tools?

No. It is a planning aid and teaching tool. Always verify performance, fuel, weather, and operating limits with approved aircraft data, charts, and operational procedures.

6. What happens if crosswind is too strong?

If crosswind exceeds the available true airspeed component needed to hold the course, the exact track may be impossible. The calculator warns you when that condition appears.

7. Should I use true or magnetic directions?

Use one consistent reference for both course and wind direction. Mixing true and magnetic values introduces error, even when every other input is correct.

8. When should I recalculate?

Recalculate whenever altitude, temperature, route, or wind changes. Even moderate updates can noticeably change true airspeed, heading correction, estimated ground speed, and en route time.