Learn how to read knots on an airspeed indicator and decode aviation wind reports, including KIAS, gusts, direction and common mistakes.
In aviation and real-world flying, a knot is one nautical mile per hour. Read 120 KIAS as an indicated airspeed of 120 knots; read wind 270/15 as wind from 270° at 15 knots. Airspeed and wind use the same unit, but they describe different motion and cannot usually be combined by simple addition.
What does one knot mean in aviation?
One knot, abbreviated kt, equals exactly one nautical mile per hour: 1.852 km/h or about 1.151 mph. At a groundspeed of 120 knots, an aircraft covers 120 nautical miles in one hour or 60 nautical miles in 30 minutes.
Do not say “knots per hour”. A knot is already a rate of distance per hour. The number also needs a label or context because airspeed, groundspeed and wind speed can all be expressed in knots.
| Example | How to read it | What it describes |
|---|---|---|
90 KIAS | 90 knots indicated airspeed | The airspeed shown to the pilot |
110 KTAS | 110 knots true airspeed | Speed through the air mass, corrected for air density |
GS 125 KT | 125 knots groundspeed | Speed over the ground |
24012G20KT | Wind from 240° at 12 knots, gusting to 20 | A METAR wind group |
How do you read an airspeed indicator in knots?
Read the pointer or speed tape against its knot scale, then identify whether the value is indicated, true or ground speed. The primary cockpit airspeed indication is normally treated as IAS unless the aircraft documentation labels it differently.
- Confirm the unit. Look for
KNOTS,KTor an aircraft-specific instrument label. Some historic and light aircraft have an mph scale, while dual-scale instruments may show both. - Work out each interval. On an analogue gauge, subtract two adjacent labelled values and divide by the number of equal spaces between them. Do not assume every small mark represents five knots.
- Read the pointer or tape. A pointer halfway between 80 and 90 on an evenly divided scale reads 85 knots. A glass-cockpit tape usually shows the present value against a fixed reference line.
- Use the correct speed reference. Checklist and performance speeds are normally given as indicated or calibrated airspeed. Do not substitute GPS groundspeed for a take-off, approach or stall-speed reference.
KIAS means knots indicated airspeed, not simply “speed in knots”. Our guide to KIAS, true airspeed and unit conversion explains the labels and conversions in more detail.
Coloured arcs and bugs help locate operating ranges, but their meaning depends on the aircraft. Published V-speeds and their cockpit uses should take precedence over a speed copied from another model or simulator add-on.
How do you read wind speed in knots?
Read an aviation wind report as direction first and speed second. Wind direction states where the wind is coming from, while the speed is given in knots.
27015KTmeans wind from 270° at 15 knots. It is blowing from the west towards the east.18012G20KTmeans wind from 180° at 12 knots, with gusts reaching 20 knots.VRB03KTmeans the direction is variable and the speed is three knots.00000KTmeans calm wind.240V300after the main wind group means the direction varies between 240° and 300°; it is not another speed.
In METAR and TAF text, wind direction is referenced to true north. Winds passed operationally by a tower or over ATIS are normally aligned with magnetic runway use, so do not compare the numbers blindly. Simulator weather systems and add-ons can also present different references. See our METAR wind-group breakdown for complete report examples.
A mistake we see constantly is treating 270° as the direction towards which the wind travels. Aviation weather uses the source direction; our explanation of reported wind direction shows how to relate it to runways and headings.
Can you add wind speed to airspeed?
You can combine wind with true airspeed to estimate groundspeed, but only as a vector; indicated airspeed is not the correct value for that calculation. Direction matters as much as wind speed.
In a simplified example, 100 KTAS with a direct 20-knot headwind produces about 80 knots groundspeed. The same aircraft with a direct 20-knot tailwind produces about 120 knots groundspeed. A crosswind changes the required heading and contributes only part of its speed to the along-track result.
If the instrument shows 100 KIAS, you cannot automatically subtract a 20-knot headwind and claim 80 knots groundspeed. IAS and TAS differ as altitude, temperature and compressibility effects increase.
Which knot reading should you use?
Use the speed appropriate to the task: indicated airspeed for flying the aircraft, true airspeed for navigation calculations, groundspeed for progress over the ground, and reported wind speed for runway and route planning.
- Take-off, approach and aircraft limitations: use the specified indicated or calibrated airspeed.
- Time and distance calculations: use groundspeed.
- Wind correction: combine forecast or observed wind with true airspeed and track.
- Flight simulators: check both the aircraft gauge and weather interface units. A global preference for knots may not change a historically accurate mph instrument, and a weather field set to km/h must not receive an unchanged knot value.