Mach to TAS Converter
Convert a cruise Mach to true airspeed at any flight level — using ISA temperature or the actual OAT — the dispatcher's everyday arithmetic.
M0.78 at FL360 standard is 447 kt — but on an ISA+15 day it's 459. Warm air aloft makes the same Mach genuinely faster over the air mass, which is why dispatch watches tropopause temperatures.
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 a cruise Mach to true airspeed at any flight level — using ISA temperature or the actual OAT — the dispatcher's everyday arithmetic.
About Mach to TAS Converter
Flight plans file Mach; everything downstream — ETAs, fuel, crossing estimates — needs knots. This converter does the dispatcher's daily sum: ISA temperature at the flight level (correctly floored at −56.5 °C above the tropopause), adjusted by the forecast deviation, into a local speed of sound, times your Mach. The nm-per-minute output feeds directly into estimate arithmetic.
How to use Mach to TAS Converter
- 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 OAT = ISA(FL) + dev (ISA floor −56.5 °C above FL360); TAS = M × 38.97√(OAT+273) substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Mach to TAS Converter?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula OAT = ISA(FL) + dev (ISA floor −56.5 °C above FL360); TAS = M × 38.97√(OAT+273) with sources cited on the page
- ✓M0.78 at FL360 standard is 447 kt — but on an ISA+15 day it's 459. Warm air aloft makes the same Mach genuinely faster over the air mass, which is why dispatch watches tropopause temperatures.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
What is Mach 0.78 in knots?+
Depends on the temperature: 447 kt TAS at FL360 on a standard day (−56.5 °C), 452 kt at ISA+5, and about 470 kt down at FL280 where the air is warmer. The Mach-to-knots question has no single answer — which is precisely why this tool asks for the level and deviation.
Why does TAS stop falling with altitude above FL360?+
The ISA tropopause: temperature stops lapsing at −56.5 °C around 36,089 ft and holds isothermal through the lower stratosphere. Since the speed of sound follows temperature alone, a given Mach yields the same TAS at FL370 and FL410 on a standard day — the tool's floor encodes exactly this.
How do strong temperature deviations change the picture?+
Roughly 1 kt of TAS per degree per Mach-0.8: an ISA+10 layer adds ~9 kt to M0.78. Over an ocean crossing that's 5+ minutes and meaningful fuel either way. Tropical tropopauses run high and cold, polar ones low and warm — dispatch temperature forecasts are TAS forecasts in disguise.
Is filed Mach the same as ground speed for estimates?+
Never — wind sits between them. The chain is Mach → TAS (this tool) → GS = TAS ± wind component. Jet-stream tailwinds of 100+ kt mean a 447-kt TAS can be a 560-kt GS eastbound and 350 westbound on the same day: the wind term dominates planning at cruise altitudes.
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