Ground Speed Calculator
Solve the complete wind triangle. Enter true airspeed, desired course, and wind to get ground speed, the heading to fly, wind correction, flight time, and ETA.
Plan the track across the ground, not just the speed through the air
The aviation mode balances the aircraft velocity against the wind vector so the resulting ground track follows your chosen course. Wind direction means where the wind is blowing from, and every direction in this calculator is referenced to true north.
Already know distance and elapsed time? Switch to the measured-trip mode for a direct average ground-speed calculation.
How to use the ground speed calculator
- Enter true airspeed: Use TAS for the altitude and power setting you plan to fly, not indicated airspeed from the instrument.
- Set the desired course: This is the track you want to make good across the ground, measured clockwise from true north.
- Enter wind from: Use the direction the wind originates from and its speed at your planned altitude.
- Add distance if useful: The calculator turns ground speed into en-route time and combines that with departure time for an ETA.
- Fly the heading, monitor the track: The required heading includes the wind correction; actual conditions still need in-flight verification.
Ground speed and wind-triangle formulas
Ground speed is the magnitude of the aircraft's velocity over the ground. With wind, it is a vector problem: true airspeed points along the heading, the wind pushes the aircraft, and the sum must point along the desired course.
Vground = Vaircraft + Vwind
Crosswind = W × sin(wind from - course)
WCA = sin-1(crosswind / TAS)
GS = TAS × cos(WCA) - headwind
GS = distance / elapsed time
The crosswind sign tells you which way to correct: positive is wind from the right and a right correction; negative is wind from the left and a left correction. A positive headwind component subtracts from forward progress, while a tailwind appears as a negative headwind and increases ground speed.
All angular inputs need the same north reference. This page uses true bearings because forecast and METAR wind directions are normally reported relative to true north. ATIS and ASOS/AWOS voice winds may be magnetic, so convert them before combining them with a true course.
Worked wind-triangle examples
These cases show what changes when the same aircraft meets headwind, tailwind, or crosswind.
| Scenario | Inputs | Heading | Ground speed |
|---|---|---|---|
| No wind | TAS 120 kt, course 090° | 090°T | 120 kt |
| 20 kt headwind | Wind 090° at 20 kt | 090°T | 100 kt |
| 20 kt tailwind | Wind 270° at 20 kt | 090°T | 140 kt |
| FAA handbook example | Course 090°, wind 045° at 40 kt | 076°T | 88 kt |
The final row is the worked wind-triangle example from Chapter 16 of the FAA Pilot's Handbook of Aeronautical Knowledge. The calculator keeps decimal precision internally and displays 76.4°T and 88.3 kt.
What changes the real ground speed?
Wind changes with altitude
Surface wind is rarely the right input for cruise. Use the forecast wind at the altitude and time of the leg.
TAS is not IAS
Indicated airspeed is an instrument pressure reading. Flight-planning wind triangles use true airspeed.
Forecasts are not steady vectors
Gusts, gradients, turbulence, and route changes make actual ground speed vary throughout the flight.
Frequently Asked Questions
What is the difference between indicated airspeed, true airspeed, and ground speed?
Indicated airspeed is the reading shown by an aircraft's airspeed indicator. True airspeed is its corrected speed through the surrounding atmosphere, while ground speed is how quickly the airplane moves across the Earth, which is the motion a GPS can measure. Wind carries the air mass, so a headwind lowers ground speed, a tailwind raises it, and a crosswind changes both the heading required and the forward speed available. The same distinction applies to a drone or other unmanned aircraft.
Can ground speed be higher than true airspeed?
Yes. A tailwind adds velocity along the course, so ground speed can be well above true airspeed. The gain depends on wind speed and the forward wind component. With a direct 20-knot tailwind, an aircraft at 120 knots TAS makes 140 knots over the ground. A headwind does the opposite. The relationship is the same in miles per hour or kilometers per hour, provided the pilot uses one unit consistently.
Does wind direction mean from or toward?
In aviation weather reports, the stated bearing is where the wind originates. Wind reported as 270° comes from the west and blows toward the east. The calculator reverses that direction internally when it constructs the wind velocity vector.
Why are the course and heading different?
Course is the path you want across the ground. Heading is where the nose points. In a crosswind, the nose must point into the wind so the combined aircraft and wind vectors produce the planned course. Their angular difference is the wind correction angle. A wind triangle is the standard navigation calculation behind that result, whether it is solved during flight planning or with a flight computer.
What happens if the crosswind is stronger than the true airspeed?
No heading can cancel enough sideways motion to hold the requested track. The calculator reports that the course cannot be maintained. It also rejects a solution when the remaining forward component is zero or negative. A navigation system can display the resulting drift, but it cannot overcome that physical limit.
How accurate are the flight time and ETA?
They are exact for the numbers entered, but the inputs are estimates. Wind varies with position, altitude, and time; true airspeed changes with power and conditions; and the flown route may differ from the planned distance. Adding the calculated flight time to the departure time gives an estimated arrival. Recalculate with current weather data because changing conditions can affect both the estimate and fuel consumption, and keep adequate fuel and time margins.
Sources and direction conventions
The calculation and default worked example follow the FAA's wind-triangle method. The weather convention comes from FAA guidance: reported wind direction is where the wind blows from, normally referenced to true north for METAR observations.
- FAA Pilot's Handbook of Aeronautical Knowledge, Chapter 16: Navigation — wind triangle, heading, course, and ground speed.
- FAA Aeronautical Information Manual, Chapter 7, Section 1 — aviation weather products and wind reporting.
- FAA Order JO 7900.5D, Surface Weather Observing — formal wind-direction and true/magnetic reporting conventions.
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