Density Altitude Calculator

Density altitude is the altitude the air *feels* like to your engine. Enter the temperature, the altimeter setting or station pressure, your field elevation and the dewpoint — this returns your DA in feet, the actual air density, grains of water, and the ET and trap correction factors that go with it.

How density altitude is calculated

Air density comes from three things: pressure pushes molecules together, heat pushes them apart, and water vapour displaces them. Combine them and you get the actual density of the air the engine is breathing. Density altitude is then just that density expressed as a height — the altitude in a standard atmosphere where the air would be this thin.

The chain is standard meteorology, not anything exotic: vapour pressure from the dewpoint via the Magnus relation, humid air density from Dalton's law of partial pressures, and then the international standard atmosphere's density law inverted to turn that density back into feet. Every step is public and independently checkable.

What it costs you on the strip

Thin air means less oxygen, less power, and less drag — but the power loss dominates, so ET goes up and trap speed goes down. NHRA publishes correction factors for exactly this, which is what the ET factor above uses. Roughly, going from sea level to Denver-height air costs a naturally aspirated car around 6% of its ET: a 12.00-second car runs about 12.76 there.

Forced induction changes the picture. A turbo or supercharged engine targets a manifold pressure, so it recovers much of what thin air takes and loses far less than the published factors suggest. The factors above are the naturally aspirated ones — treat them as an upper bound on a boosted car's loss, not a prediction.

A standard day is not zero

Enter 60 °F, 29.92 inHg, dry, at sea level — the motorsports standard day — and this calculator returns about 68 feet, not zero. That is correct. The motorsports standard atmosphere is defined at 60 °F while the aviation standard atmosphere that DA is measured against uses 59 °F, so the motorsports reference day is about 0.2% less dense and sits slightly "above" sea level. It is a small, deliberate quirk of using the drag-racing convention.

Common questions

What is a good density altitude for drag racing?

Lower is faster. Below about 1,000 ft DA is good air and cars run near their best; 3,000–5,000 ft costs noticeable ET; above 6,000 ft is thin and everything slows down. Negative DA — a cold, dry, high-pressure night near sea level — is the quickest air you will ever see, and it is why records fall in winter.

Why is density altitude higher than my actual elevation?

Because heat and humidity both thin the air. On a hot, humid day a sea-level track can easily read 3,000 ft or more of density altitude — the air behaves as if the track had been lifted that far up. Only on a cold, dry, high-pressure day does DA drop near or below your true elevation.

Does humidity really matter?

Yes, though less than temperature. Water vapour is lighter than dry air, so humid air is less dense, not more. The effect is small compared to a 20-degree temperature swing but it is real, and this calculator accounts for it through the dewpoint.

Should I use altimeter setting or station pressure?

Use whichever you have. Weather apps and METAR reports give an altimeter setting, which is corrected to sea level — pair it with your field elevation and the calculator converts it. A trackside weather station usually gives absolute station pressure, which needs no elevation at all.