# How to calculate mach based on IAS?

It doesn’t show the cruising IAS.

Referring to your original post. You seem to have mixed up Ground Speed and Initial Air Speed. Are you sure that you have done the calculations correctly?

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I am using a converter

Which speed are you converting to?

And what speed result are you aiming for?

I want to see what IAS is M 0,54

@Philippe_Gilbert Are you talking about the Dash-8 calculations from your previous topic?

Ground speed is your speed relative to the ground. If you’re traveling in a car down the highway and look at the speedometer to see your speed, that’s ground speed. Your car is moving 60mph/100kmh relative to the ground.

IAS stands for indicated airspeed. This number will decrease as you gain altitude and increase as you lose altitude, even if your ground speed (speed relative to the ground) remains constant.

The Mach number is a percentage of the speed of sound. Mach 0.54 means 54% the speed of sound. As you increase altitude, the air becomes less dense, so sound travels slower. This means that even if you’re ground speed remains constant, your mach # will increase as you gain altitude.

Long story short, the IAS for M0.54 changes depending on what altitude you’re flying at.

You may find this tutorial helpful: Understanding different types of speeds

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Could you share the converter you are using as well as the information you are inputting?

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Around 206IAS. General rule for IF is every 5 IAS is another .01 Mach

The IAS only starts decreasing at 28000ft

How about the second part of my question?

wait, let me check.

Winds can be part of this.

No, since i’m not using GS

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Is the calculator you’re using even giving you indicated airspeed? Calibrated, equivalent, and true airspeed are different from IAS.

And FYI, you usually don’t need to know the IAS at cruise if you have the Mach speed. Your Mach speed is always shown here in HUD/Cockpit view:

Actually there aren’t many that cruise at m0.86. Planes like the a320 and 737 cruise at 0.78. The only ones I know that cruise at 0.85 are the 747(all versions) and 787.

You could probably try this:

The post above will probably also make you realize that it’s a bit more complicated than to just say that X knots IAS equals X in mach speed :)

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The Dash 8 shouldn’t be cruising at an altitude where you see Mach speeds. It cruises between 300-360 knots.

here is the issue: M 0.78 is 290kts IAS in IF however my converter shows that M 0.78 is 295kts IAS. However, when I go to that speed in IF, it gives me M 0.79

The issue here is, as others have told you - is that it’s not as black & white as you put it out to be. Your calculator doesn’t even calculate IAS. It’s not an option.

The IAS can differ depending on atmospheric conditions.

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