True Airspeed
Calibrated airspeed + pressure altitude + OAT → true airspeed. Precise density formula and the 2% rule-of-thumb side by side, with Mach number above FL180.
Inputs
From your ASI, corrected for instrument + position error. For most GA aircraft, IAS ≈ CAS within a knot or two.
Set altimeter to 29.92 and read indicated altitude. Or use field elevation + (29.92 − altimeter setting) × 1000.
Outside air temperature from the OAT probe. Used for the precise density calc.
Verdict
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Enter CAS, pressure altitude, and OAT
CAS ÷ √σ — accounts for both pressure altitude AND temperature.
CAS × (1 + 0.02 × alt/1000). Ignores temperature. Quick mental math.
What altitude the airplane thinks it's at — directly drives engine + wing performance.
About this calculator
The precise TAS uses the NACA 1235 standard atmosphere: density altitude from DA = PA + 120 × (OAT − ISA), then σ = (1 − DA × 6.875e-6)^4.2561, then TAS = CAS / √σ. The rule-of-thumb is the 2%-per-1000-ft approximation from the FAA Pilot's Handbook — accurate enough to back up the precise figure when you don't have an OAT probe.
Mach surfaces only at FL180+ because that's where the variation in speed of sound with OAT starts to matter operationally. Below FL180 it's a curiosity, not a limit.
Trim
Performance planning for the stage check? Trim keeps the whole syllabus on track — not just one calculation.
Flight training management for independent CFIs.