Ground Speed Calculator
Calculate aircraft ground speed from true airspeed and wind, or find speed from distance and time in knots, km/h, mph, and m/s.
🌍 What is the Ground Speed Calculator?
Ground speed is the speed of an aircraft measured relative to the ground beneath it, as opposed to airspeed, which is measured relative to the surrounding air mass. The difference between the two is always the wind. Understanding this distinction is fundamental to flight planning: an aircraft's fuel burn is determined by airspeed and time, but the distance covered over the ground is determined by ground speed.
The Aviation mode of this calculator solves the classic wind triangle problem used by every pilot on every cross-country flight. You enter your true airspeed, your desired heading, and the wind speed and direction. The calculator returns your ground speed, your actual track over the ground, and the wind correction angle you need to apply to maintain that track. This is the same math performed by an E6B flight computer or flight management system, applied instantly.
The Simple mode is useful for any situation where you know a distance and the time it took to cover it: a road trip, a boat crossing, a cycling segment, or calculating average speed from GPS data. Enter the distance and time, select your preferred speed unit, and the calculator returns the result simultaneously in knots, km/h, mph, and m/s for easy comparison.
Pilots use this tool during preflight planning to estimate en-route times, fuel requirements, and cruise altitudes. Student pilots use it to understand the wind triangle before progressing to E6B or digital FMS practice. Sailors navigating coastal waters use the aviation mode to understand set and drift. Anyone who needs a quick distance-over-time calculation can use the simple mode with any unit system.
📐 Formula
GS = √(TAS² + WS² − 2 × TAS × WS × cos(θ))
GS = ground speed (knots)
TAS = true airspeed (knots)
WS = wind speed (knots)
θ = angle between heading vector and wind vector
Example: TAS 150 kt, heading 090°, wind 270° at 20 kt (direct tailwind): GS = sqrt(150² + 20² + 2 x 150 x 20) = 170 kt
WCA = arcsin(WS × sin(α) ÷ TAS)
WCA = wind correction angle (degrees to crab into wind)
α = angle between desired track and wind direction
Example: 20 kt crosswind, TAS 150 kt: WCA = arcsin(20/150) ≈ 7.7° into wind
GS = Distance ÷ Time
GS = ground speed in selected unit
Distance = nautical miles, km, or miles
Time = hours
Example: 300 nm in 1.5 hours = 200 kt ground speed
📖 How to Use This Calculator
Aviation Mode: Find Ground Speed from TAS and Wind
1
Choose Aviation mode - Select the Aviation (TAS + Wind) tab at the top of the calculator.
2
Enter true airspeed and heading - Input your cruise TAS in knots and your intended magnetic heading in degrees (0 to 360).
3
Enter wind speed and direction - Wind direction uses the meteorological FROM convention (270 means wind blowing FROM the west). Enter these from your ATIS or weather briefing.
4
Read ground speed, track, and WCA - The results show ground speed in knots, your actual ground track, and the wind correction angle to apply.
💡 Example Calculations
Example 1 - Direct Tailwind: 150 kt TAS, Heading 090, Wind 270 at 20 kt
Wind directly behind the aircraft (180 degrees off heading)
1
Wind from 270° means it blows eastward. Heading 090° also points east. Pure tailwind.
2
GS = TAS + wind component = 150 + 20 = 170 kt
3
Wind correction angle = 0° (wind directly behind, no crab needed)
Result = 170 kt ground speed, track 090°, WCA 0°
Try this example →Example 2 - Direct Headwind: 150 kt TAS, Heading 090, Wind 090 at 30 kt
Wind directly into the aircraft nose
1
Wind from 090° blows westward, opposing heading 090°. Direct headwind.
2
GS = TAS - headwind = 150 - 30 = 120 kt
3
Track remains 090°, WCA = 0° (no drift, just slower)
Result = 120 kt ground speed, track 090°, WCA 0°
Try this example →Example 3 - Simple Speed: 450 nm in 2.25 hours
Calculate ground speed from GPS log or flight plan comparison
1
Switch to Simple mode, select Knots unit
2
Distance = 450 nm, Time = 2.25 hours
3
GS = 450 / 2.25 = 200 kt = 370.4 km/h = 230.2 mph
Result = 200 kt, 370.4 km/h, 230.2 mph
Try this example →❓ Frequently Asked Questions
What is the difference between ground speed and airspeed?
Airspeed measures the aircraft's speed relative to the air around it. Ground speed measures the aircraft's speed relative to the ground below. Wind is the difference. A 200 kt aircraft in a 40 kt headwind moves over the ground at only 160 kt. The same aircraft with a 40 kt tailwind has a ground speed of 240 kt. Fuel burn tracks airspeed; arrival time tracks ground speed.
How do I find ground speed without a GPS?
Use the wind triangle method: true airspeed plus wind vector equals ground speed vector. Enter your TAS, heading, wind speed, and wind direction into the Aviation mode of this calculator. The result is your estimated ground speed and track. This is the same method used on the E6B circular slide rule that pilots have used since the 1930s.
What does wind FROM 270 degrees mean?
Meteorological convention reports wind as the direction from which the wind originates, not where it is going. Wind from 270 (west) blows eastward. Wind from 000 or 360 (north) blows southward. This calculator uses the standard meteorological FROM convention for all wind direction inputs, matching ATIS, METAR, and weather briefing reports.
What is wind correction angle and why does it matter?
Wind correction angle (WCA) is how many degrees you must point the aircraft into the wind to compensate for drift. Without it, crosswind pushes you off track. If WCA is 8 degrees left, you fly a heading 8 degrees to the left of your desired track. The calculator computes WCA automatically so you can set the correct heading for your desired ground track.
How does a crosswind affect ground speed?
A pure crosswind (90 degrees from the heading) slightly reduces ground speed because you must crab into it, and the effective forward component of airspeed is TAS times cosine of WCA. For a 20 kt crosswind on a 150 kt TAS aircraft, WCA is about 7.7 degrees and ground speed is about 148 kt. The headwind component is more significant than the crosswind speed reduction.
How do I convert knots to kilometers per hour?
Multiply knots by 1.852 to get km/h. One knot is one nautical mile per hour, and one nautical mile is 1.852 km. For example, 120 kt = 120 x 1.852 = 222.2 km/h. Alternatively, use the Simple mode of this calculator: enter any distance and time to see all four speed units simultaneously.
What is the formula for ground speed in aviation?
The exact formula uses the law of cosines applied to the wind triangle: GS = sqrt(TAS squared + WS squared - 2 times TAS times WS times cosine of angle between heading and wind-to direction). For pure tailwinds, GS = TAS + WS. For pure headwinds, GS = TAS - WS. For crosswinds, the reduction is smaller but the wind correction angle becomes significant.
What units are used for aviation speed measurement?
Aviation worldwide uses knots (nautical miles per hour, kt or kts) for airspeed and ground speed. A knot is exactly 1.852 km/h or 1.15078 mph. Altitude is measured in feet in most countries (meters in Russia and China). Distance on flight plans is in nautical miles. Runway visual range may be in meters or feet depending on country.
How does altitude affect ground speed?
Altitude affects airspeed calibration but not the wind triangle math. At higher altitudes, air is thinner, so at the same power setting an aircraft achieves a higher TAS than at sea level for the same indicated airspeed. Winds aloft are typically stronger at altitude, which can significantly affect ground speed. This calculator uses TAS directly, already corrected for altitude effects.
Can I use this calculator for maritime navigation?
Yes. The aviation mode applies equally to vessels. Enter your boat's speed through water (equivalent to TAS) and your heading, then enter the current speed and current direction (FROM convention). The result is your speed over ground and the set and drift equivalent of wind correction angle. Use the simple mode for distance-over-time speed calculations from GPS or chart measurements.
How do I calculate flight time from ground speed?
Flight time = Distance / Ground Speed. For example, a 450 nm flight at 200 kt ground speed takes 2.25 hours (135 minutes). If ground speed varies due to changing winds, calculate each segment separately and sum the times. Always add extra fuel for headwinds: plan for a lower ground speed than forecast to have a safety margin.
What is the E6B flight computer and how does this compare?
The E6B is a circular slide rule invented in 1940 for airborne navigation calculations including the wind triangle, time-speed-distance, and unit conversions. This calculator applies the exact same math digitally, with instant results and no mechanical manipulation. Student pilots often learn on the E6B to understand the underlying trigonometry before transitioning to digital tools or flight management systems.