Ground Speed Calculator

Indicated airspeed (IAS) is what the airspeed indicator shows; true airspeed (TAS) is the aircraft's actual speed through the air mass after correcting for altitude and temperature; ground speed (GS) is the aircraft's speed over the ground — TAS plus the wind's effect, solved with the wind triangle. Example: at 120 kt TAS with a 20 kt headwind straight on the nose, this calculator gives a ground speed of 100.0 kt. Density-altitude-lab shows a simple TAS-minus-headwind readout; this tool solves the full wind triangle including crosswind and wind correction angle.

The wind triangle adds three vectors tip-to-tail: the heading/TAS vector (where the nose points and how fast the aircraft moves through the air), the wind vector, and the resulting track/ground-speed vector. The exact relations are GS = √(TAS² + WS² + 2·TAS·WS·cos δ) and WCA = atan2(WS·sin δ, TAS + WS·cos δ), where δ is the angle between the wind's TO-direction and your heading. Example: 120 kt TAS with 20 kt of wind at exactly 90° to the heading gives GS = 121.66 kt with a 9.46° drift angle — the diagram above draws this triangle for your own numbers.

The wind correction angle — also called the crab angle — is how many degrees you must point the nose into the wind so the aircraft actually tracks the course you want. In “Course→Heading” mode this calculator solves it exactly as WCA = asin(crosswind ÷ TAS). Example: to hold a 090° course at 120 kt TAS with wind from 000° at 20 kt, steer 80.4° (about 9.59° into the wind) and your ground speed will be 118.32 kt. In “Heading→Track” mode it instead reports the drift angle the wind imposes on the heading you fly.

On the wind side of an E6B you plot the wind vector from the center grommet, rotate the azimuth plate so your course is under the true index, then slide the card until the wind dot sits on your TAS arc — the grommet then reads ground speed and the dot's lateral offset reads the correction angle. This calculator performs the same vector addition exactly: for instance it reproduces the E6B answer of 100.0 kt ground speed for 120 kt TAS into a 20 kt headwind, and 140.0 kt with that wind on the tail.

Only the along-track component of the wind changes your ground speed; the cross-track component only pushes you sideways (which the correction angle fixes). A 20 kt wind at 45° to your heading costs just 13.20 kt: 120 kt TAS becomes 106.80 kt ground speed, not 100 kt. That is why a quartering headwind hurts far less than the windsock suggests — and why the exact wind triangle beats the rough TAS-minus-wind shortcut.

Yes — any tailwind component adds directly to ground speed. At 120 kt TAS with 20 kt of wind dead on the tail, ground speed is 140.0 kt, faster than the aircraft is moving through the air. That is free speed: a 300 NM leg takes 2 hr 8 min instead of 3 hr 0 min, which is also why flight plans are built around forecast winds aloft, not just still-air TAS.

Time = distance ÷ ground speed, so wind swings the ETA directly. A 300 NM leg at 120 kt TAS takes 3 hr 0 min into a 20 kt headwind (GS 100.0 kt) but only 2 hr 8 min with a 20 kt tailwind (GS 140.0 kt) — nearly an hour apart on the same route. The flight-time readout above does this division for any distance in NM, km, or miles, using the wind-corrected ground speed rather than TAS.

That tool (tool #146) shows ground speed as a simple readout of TAS minus a headwind number — it never solves the wind triangle, so it cannot handle crosswinds or tell you a correction angle. This calculator is the dedicated wind-triangle solver: TAS plus a full wind vector gives wind-corrected ground speed, drift/crab angle, and headwind, tailwind, and crosswind components. Use them together: density-altitude-lab for how the air performs, this tool for where the wind takes you. See also the crosswind component calculator for runway crosswind limits.

True airspeed and wind speed accept knots, km/h, mph, and m/s; distance accepts nautical miles, kilometers, and statute miles. Results always show ground speed in both knots and km/h. Conversions are exact definitions: 1 kt = 1.852 km/h, so 100 mph is 86.90 kt. Headings, courses, and wind directions are degrees from 000° to 360°, with wind given FROM (the meteorological convention, as in a METAR).