Calculator inputs
Use pressure mode for pitot-static data, or correction mode to move between IAS and CAS using signed correction values.
Example data table
These sample rows illustrate how impact pressure, altitude, temperature, and correction inputs can change IAS, CAS, TAS, and Mach.
| Case | Impact Pressure (Pa) | Pressure Altitude (ft) | OAT (°C) | Total Correction (kt) | IAS (kt) | CAS (kt) | TAS (kt) | Mach |
|---|---|---|---|---|---|---|---|---|
| Training approach | 1,500 | 0 | 15 | 1.5 | 94.44 | 95.94 | 95.94 | 0.1450 |
| Short cross-country | 3,200 | 5,000 | 5 | 2.0 | 137.72 | 139.72 | 150.33 | 0.2313 |
| Mountain cruise | 6,200 | 12,000 | -5 | 2.5 | 190.99 | 193.49 | 232.68 | 0.3646 |
| High-altitude transit | 9,500 | 18,000 | -15 | 3.0 | 235.21 | 238.21 | 314.26 | 0.5019 |
Formula used
1) Impact pressure
qc = pt - ps
2) Mach number from pitot-static pressure
M = √{5 × [((qc/ps) + 1)2/7 - 1]}
3) Calibrated airspeed from sea-level reference calibration
CAS = a0 × √{5 × [((qc/p0) + 1)2/7 - 1]}
4) Indicated airspeed after corrections
IAS = CAS − instrument correction − position correction
5) True and equivalent airspeed
TAS = M × √(γRT) and EAS = TAS × √(ρ/ρ0)
6) Low-speed check
V ≈ √(2qc/ρ0) for low Mach conditions where compressibility is small.
Positive entered corrections are defined as values added to IAS to obtain CAS. That convention keeps the workflow consistent across the two calculator modes.
How to use this calculator
Step 1
Choose Pressure to IAS when you know pitot-static pressure information. Choose IAS/CAS correction when you already have IAS or CAS and only need the corrected counterpart.
Step 2
Set the display speed unit first. Instrument correction and position correction use that same speed unit, so keep the sign and unit system consistent.
Step 3
Provide either pressure altitude or static pressure. Pressure altitude is usually faster for standard flight calculations, while static pressure is useful when raw sensor data is available.
Step 4
Enter outside air temperature when known. If you leave it blank, the calculator uses ISA temperature for the selected pressure condition and still computes TAS and density.
Step 5
Review IAS first, then compare CAS, EAS, TAS, Mach, density ratio, and the low-speed approximation. Use the export buttons to save a report for design notes or flight analysis.
Frequently asked questions
1) What is indicated airspeed?
Indicated airspeed is the speed shown directly on the airspeed indicator. It is the cockpit reading before correcting for position error, instrument error, or actual air density differences.
2) Why can IAS differ from CAS?
CAS applies corrections for instrument and installation effects. Small differences are common, especially at lower speeds, unusual attitudes, flap changes, or imperfect static-source locations.
3) Why does TAS become higher than IAS at altitude?
As altitude rises, air density drops. The aircraft must move faster through thinner air to create the same dynamic pressure, so TAS increases while IAS can stay nearly unchanged.
4) When does compressibility matter?
Compressibility becomes increasingly important as Mach rises, especially above roughly Mach 0.3. That is why this calculator uses the compressible pitot-static relation instead of only the simple low-speed approximation.
5) Should I enter static pressure or pressure altitude?
Use pressure altitude when working from common flight or performance data. Use static pressure when you have direct sensor readings from a test setup, logger, or instrumentation system.
6) What sign should I use for corrections?
Enter corrections as values added to IAS to obtain CAS. Positive values mean the corrected calibrated speed is higher than the raw indicated speed.
7) Can I use this for every aircraft?
It is a solid engineering calculator, but it does not replace aircraft-specific handbook data, calibration charts, or approved avionics logic. Always verify critical operating speeds with the proper flight documentation.
8) What are the CSV and PDF buttons for?
They export the calculated result set so you can store test cases, attach reports, compare scenarios, or document design reviews without retyping the airspeed output manually.