How to use this calculator
- Enter EAS or approximate CAS. Use equivalent airspeed when available.
- Enter pressure altitude. Use pressure altitude, not field elevation unless they match.
- Enter OAT. Use outside air temperature in degrees C.
- Read TAS. Treat the result as a rough planning estimate.
How it works
The page estimates air density from ISA pressure at the entered pressure altitude and actual OAT. Then it applies TAS = EAS / sqrt(sigma), where sigma is density ratio.
Use TAS with turn radius, standard-rate turn and range and endurance.
Worked example
Verified against the live calculator
At 100 kt equivalent airspeed, 5,000 ft pressure altitude and 5 C OAT, the TAS estimate is roughly 108 kt.
Frequently asked questions
How is TAS estimated?
The calculator estimates density ratio from pressure altitude and OAT, then uses TAS = EAS / sqrt(density ratio).
Can I enter CAS instead of EAS?
For low-speed screening, CAS is often close enough to EAS for a rough estimate, but exact conversion needs aircraft and air-data corrections.
Why does TAS rise with altitude?
Air density decreases with altitude and temperature, so the same dynamic pressure corresponds to a higher true airspeed.
Does this include compressibility?
No. It is a simple density-ratio estimate, not a full air-data computer.
Method & assumptions
- Uses an ISA pressure estimate and ideal-gas density from entered OAT.
- Does not include position error, instrument error, compressibility correction or aircraft-specific CAS/EAS tables.