The density altitude calculator works out relative humidity and absolute pressure from the values you supply. Enter air temperature, alpha, altimeter setting, expo, station elevation, and the calculator applies the standard relationship straight away, so you get the answer without working through the algebra yourself.
What Is the Density Altitude Calculator?
It is built around relative humidity, absolute pressure, relative density, and it works the same way whether you are checking a homework answer, confirming a colleague's figure, or working something out for yourself. Everything runs in your browser, so nothing you enter is uploaded anywhere.
How the Density Altitude Calculation Works
Nothing is hidden: each output is worked out from the values above it, which makes it easy to see where a surprising answer came from.
The relationship between air temperature, alpha, altimeter setting, expo, station elevation and relative humidity, absolute pressure, relative density, density altitude, pv corrections, air density, dew point, pv, pd is fixed, so the same figures always give the same answer. That makes it a good cross-check: run the numbers a second way and see whether the result agrees.
Getting a Result You Can Trust
Start with a set of figures you are confident about. If one of the air temperature or alpha or altimeter setting or expo or station elevation values looks wrong, the result will be wrong too, because everything downstream is built on top of it. Work through the outputs one at a time and check that each one is the size you would expect before relying on the last figure.
Frequently Asked Questions
What do I need to work out relative humidity?
Enter air temperature, alpha, altimeter setting, expo, station elevation. The calculator then works through the relationship and reports relative humidity, absolute pressure, relative density.
What does the density altitude actually calculate?
It takes air temperature and alpha and altimeter setting and expo and station elevation and converts them into relative humidity, absolute pressure, relative density using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter air temperature?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Why does a small change in one value move the answer so much?
That happens when an output depends on a ratio, because dividing by a small number magnifies any change in it. Check the units first, then check whether the value you entered is in the range the relationship was designed for.
Can I use this for a quick estimate as well as a precise answer?
Yes. The calculator is built for quick checks, so round your inputs to a sensible number of significant figures and the result will be just as useful. If you need more precision, keep the same method and add digits to the inputs rather than adjusting the method itself.