Density Altitude & Pressure Altitude Calculator

What density altitude is

Density altitude is pressure altitude corrected for non-standard temperature. Put simply, it is the altitude your aircraft and engine actually feel. Air density falls as temperature rises, so on a hot day the air is thinner than the standard atmosphere assumes and the aircraft behaves as if it were much higher than the field elevation on the chart. Density altitude is the single number that captures that effect, which is why aircraft performance charts are built around it rather than around raw field elevation.

High density altitude and aircraft performance

A high density altitude means less dense air, which means less power from the engine, less thrust from the propeller, and less lift from the wing. The practical results on a high density altitude day are:

• Longer takeoff and landing rolls — the wing needs more true airspeed to fly, so you use more runway.
• Reduced rate of climb — a normally aspirated engine makes less power, and the climb gradient suffers most where terrain matters most.
• Higher true airspeed for a given indicated airspeed — approaches feel fast and floaty even though the airspeed indicator reads normal.

Hot-and-high operations — high-elevation airports on summer afternoons — are where density altitude bites hardest. It is routine for density altitude to sit thousands of feet above field elevation in those conditions, so always run the number and check it against your aircraft performance charts before departure.

The density altitude formula

Density altitude is built from two standard equations, and this calculator uses both — the same ones printed beneath every result:

• Pressure altitude = field elevation + (29.92 − altimeter setting) × 1,000.
• ISA temperature = 15 °C − 1.98 °C for every 1,000 feet of pressure altitude.
• Density altitude = pressure altitude + 120 × (OAT − ISA temperature).

The 120-feet-per-degree term is the standard rule of thumb for how far density altitude moves for each degree Celsius the outside air sits above standard. It is the same relationship the density altitude tab in the Sky Duty E6B uses, so the two tools agree.

How to calculate density altitude

The calculator works in two steps, using the same math as the density altitude tab in the Sky Duty E6B so the numbers stay consistent across the tools:

1. Pressure altitude = field elevation + (29.92 − altimeter setting) × 1,000. This corrects field elevation to the standard 29.92 inHg datum.
2. Density altitude = pressure altitude + 120 × (OAT − ISA temperature), where ISA temperature = 15 °C − 1.98 °C per 1,000 feet of pressure altitude.

If you already know your pressure altitude, enter it in the field-elevation box and leave the altimeter at the standard 29.92 — the result is identical to the E6B density altitude tab.

What is pressure altitude?

Pressure altitude is your altitude above the standard 29.92 inHg pressure datum, independent of temperature. It is what your altimeter reads when you set it to 29.92 (2992), and it is the altitude aircraft use above the transition altitude so everyone shares a common reference. Because it corrects field elevation to the standard datum, pressure altitude moves about 1,000 feet for every inch the altimeter setting departs from 29.92: a lower setting gives a higher pressure altitude, and on a standard-pressure day pressure altitude equals field elevation.

This page is also a pressure altitude calculator. Switch the tool above to Pressure Altitude mode and it computes pressure altitude from field elevation and altimeter setting alone — no temperature needed — using PA = field elevation + (29.92 − altimeter setting) × 1,000. In Density Altitude mode the same pressure altitude appears as its own figure alongside density altitude, ISA temperature, and ISA deviation, because pressure altitude is the first step in the density altitude calculation. If you already know your pressure altitude, enter it in the field-elevation box and leave the altimeter at 29.92.

Worked example

A field elevation of 5,000 feet with the altimeter at 29.92 inHg gives a pressure altitude of 5,000 feet. On a 25 °C day, the ISA temperature at 5,000 feet is about 5.1 °C, so the air is roughly 19.9 °C warmer than standard. Density altitude works out to about 5,000 + 120 × 19.9 ≈ 7,400 feet. In other words, at a 5,000-foot field on a warm afternoon your aircraft performs as though it were departing from roughly 7,400 feet. Push the temperature higher or add elevation and the gap widens quickly.