1. Calculating Density Altitude With a Pencil

How do we calculate density altitude? There are just two pieces of information you’ll need for a rough approximation: pressure altitude and temperature. Where do you find this information? Easy: for temperature, you look at the thermometer in your airplane. For pressure altitude, set the window in your altimeter to 29.92. Whatever value it reads is pressure altitude. Finding pressure altitude when you're not sitting in the airplane is a bit more complicated, but here’s a nifty formula: pressure altitude = (standard pressure - your current pressure setting) x 1,000 + field elevation. That’s a pretty simple formula since two of the variables will always be the same and the other two are easy enough to find. Let’s say our current altimeter setting is 29.45 and the field elevation is 5,000 feet. That means (29.92 - 29.45) x 1,000 + 5,000 = 5,470 feet. Easy! Now let’s move on to step two, finding density altitude. Here’s the formula: density altitude = pressure altitude + [120 x (OAT - ISA Temp)]. Try this formula the next few times you go flying (or, just for fun, run some scenarios using Microsoft Flight Simulator) and before you know it you’ll be able find your ballpark density altitude without digging in your flight bag for that E6B.

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