This tool uses a standard-atmosphere pressure model with actual OAT to estimate air density, then applies the common approximation: TAS = CAS ÷ √σ (or reverse), where σ is density ratio. It is for planning and learning, not certified flight operations.
What is a CAS TAS calculator?
A CAS TAS calculator helps pilots convert between Calibrated Airspeed (CAS) and True Airspeed (TAS). CAS is the speed corrected for instrument and position errors, while TAS is your real speed through the surrounding air mass. As altitude increases and air density drops, TAS becomes significantly higher than CAS for the same aerodynamic performance.
Why CAS and TAS both matter
In flight operations, each speed measure has a job. CAS is tied to aerodynamic loads and stall behavior. TAS is tied to navigation, enroute timing, and fuel planning. If you only look at one number, you risk planning errors. A good workflow is to fly target performance using indicated/calibrated speeds and plan route efficiency using true airspeed.
- CAS: useful for handling, approach targets, and structural limits.
- TAS: useful for leg time, groundspeed estimates, and range calculations.
- Groundspeed: TAS adjusted for wind, which determines actual travel over the ground.
How this calculator works
1) Pressure altitude sets pressure
The calculator first estimates atmospheric pressure from pressure altitude using a standard atmosphere model. This provides a practical baseline for converting between indicated-style speed and true airspeed.
2) OAT sets density
We then combine that pressure with your entered outside air temperature (OAT) to compute air density. Colder air is denser; warmer air is less dense.
3) Density ratio drives the conversion
The key factor is density ratio (σ), defined as local air density divided by sea-level standard density. TAS and CAS are linked by the square root of this ratio in the common planning approximation:
- TAS = CAS / √σ
- CAS = TAS × √σ
Practical pilot tips
- At higher altitudes, expect TAS to be much higher than CAS even in calm conditions.
- Use TAS for flight planning, then convert to expected groundspeed using wind forecasts.
- For safety-critical values, follow your POH/AFM and certified avionics data first.
- In high-temperature conditions, lower density pushes TAS up for a given CAS.
Example scenario
Suppose you hold 120 knots CAS at 10,000 feet on a warm day. Because density is lower than sea level, your TAS could be around 140 knots or more depending on temperature. That means your route timing and fuel burn per leg can be materially different from what CAS alone suggests.
Limitations and accuracy notes
This calculator is intentionally lightweight and uses a widely accepted approximation for general aviation planning. It does not model full compressibility effects, aircraft-specific position error curves, or transonic/high-Mach corrections. For training and routine planning, this is usually adequate. For advanced operations, use certified performance charts, onboard systems, and approved operational procedures.