Indicated Airspeed Calculator

Work out indicated airspeed instantly with clear inputs, formula shown and shareable results.

About Indicated Airspeed Calculator

This reverses the true airspeed relationship: calibrated airspeed is true airspeed multiplied by the square root of the density ratio, then the position error correction from the aircraft flight manual converts CAS to the indicated value you will see on the dial.

Formula

Indicated airspeed

CAS = TAS x sqrt(sigma); IAS = CAS + position error correction

Worked example

With the default values below, Indicated Airspeed Calculator returns Indicated airspeed of 152.74. Change any input above and every figure here is recalculated in your browser.

Inputs used

True airspeed: 180 kt
Pressure altitude: 10,000 ft
Outside air temperature: -5 °C
Position error correction: -2 kt

Results

Indicated airspeed: 152.74 kt
Calibrated airspeed: 154.74 kt
Density ratio (sigma): 0.7390
IAS / TAS ratio: 0.8485

Step by step

1Values used
2Indicated airspeed
3Indicated airspeed= 152.74 kt
4Calibrated airspeed= 154.74 kt
5Density ratio (sigma)= 0.7390
6IAS / TAS ratio= 0.8485

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Aviation results are planning estimates only. Always verify take-off, landing, fuel, weight and balance figures against the certified Aircraft Flight Manual, current performance charts and applicable aviation regulations before flight.

Frequently Asked Questions

What is position error?

Static and pitot pressure errors caused by airflow around the airframe. The AFM lists the correction, which is usually a few knots and varies with speed and configuration.

Why fly indicated rather than true airspeed?

Stall, flap and manoeuvring limits all depend on dynamic pressure, which is what the indicated reading represents, so those limits stay at the same IAS at any altitude.