True Airspeed (TAS) Calculator
Convert calibrated airspeed to true airspeed from pressure altitude and temperature — the E6B classic, exact and instant.
The wing and the pitot tube feel dynamic pressure — the same CAS means more real speed in thinner air. Roughly +2% per 1,000 ft is the rule; this is the exact version.
Formula
⚠️ For flight planning and education only — verify with your POH/AFM, certified instruments and official sources. Not for primary navigation or airworthiness decisions.
Convert calibrated airspeed to true airspeed from pressure altitude and temperature — the E6B classic, exact and instant.
About True Airspeed (TAS) Calculator
Your airspeed indicator tells a useful lie above sea level: it reports dynamic pressure, not speed. This calculator does the E6B's signature conversion — calibrated airspeed to true airspeed via the density ratio at your pressure altitude and temperature — and shows the percentage gain, the number flight planners and groundspeed estimates actually need.
How to use True Airspeed (TAS) Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula TAS = CAS / √σ; σ from density altitude (PA + 118.8 × (OAT − ISA)) substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use True Airspeed (TAS) Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula TAS = CAS / √σ; σ from density altitude (PA + 118.8 × (OAT − ISA)) with sources cited on the page
- ✓The wing and the pitot tube feel dynamic pressure — the same CAS means more real speed in thinner air. Roughly +2% per 1,000 ft is the rule; this is the exact version.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why does TAS exceed CAS at altitude?+
The indicator senses dynamic pressure ½ρV². As density ρ falls with altitude, the same indicated pressure requires a higher true V. At 8,500 ft density altitude the air is about 22% thinner, so true speed runs about 12% (1/√0.78) faster than calibrated.
What's the difference between IAS and CAS here?+
CAS is IAS corrected for your aircraft's pitot-static position error, published as a table in the POH. In cruise the difference is usually 1–2 kt for light aircraft, so feeding IAS in gives a fine planning answer; for precision (flight tests, endurance records) apply the POH correction first.
How accurate is the 2%-per-1,000 ft rule?+
Within about half a knot up to 10,000 ft on standard days — it's calibrated to the troposphere's typical density gradient. It drifts when temperature departs ISA strongly: a hot high cruise adds density altitude the rule's input (pressure altitude) doesn't see. This tool computes via density altitude, so it never drifts.
Which speed do I file in the flight plan?+
True airspeed — box (or item) 15 of the ICAO flight plan asks for cruising TAS, because ATC computes your estimates from TAS plus wind. Filing your indicated speed under-promises by 10–20% at typical cruise altitudes and quietly wrecks every time estimate downstream.
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