Free tool — the altitude your engine actually feels.
Density Altitude Calculator
Enter temperature, humidity, and station pressure — get the altitude your engine actually feels. Same math the in-app logbook uses against every run.
What is density altitude?
Density altitude is the altitude at which the atmosphere's density would match what you're seeing right now. It's the air your engine "feels" — not the elevation the GPS shows.
Hotter air, more humidity, and lower barometric pressure all make the air thinner. Thinner air means less oxygen per cubic inch, which means slower elapsed times. A naturally-aspirated car can lose 0.05 – 0.10 seconds in the quarter-mile for every 1,000 ft of DA gain. Across a single race day at the same strip, a swing from cool morning to hot afternoon often moves DA by 1,500 – 2,500 ft — enough to shift a 9-second NA car by a full tenth.
The math here uses the virtual-temperature barometric formula — the same one Kestrel meters and aviation flight computers use. Read the full deep-dive →
Inputs
Air temp (°F), relative humidity (%), TRUE station pressure (inHg). Track elevation is informational — station pressure already encodes it.
Pressure types
A Kestrel reads station pressure (~27.5″ at 2,000 ft). Weather.com shows altimeter setting (~29.84″, sea-level corrected). For DA always use station pressure.
Normal swing
A cool morning vs. hot afternoon at the same strip routinely swings DA by 1,500 – 2,500 ft. Enough to move a 9-second NA car by a full tenth.
FAQ
What pressure unit should I enter?
True station pressure (absolute) in inches of mercury — the value your Kestrel or trackside meter reads. NOT the sea-level-corrected "altimeter setting" weather.com shows. At elevation those differ significantly: roughly 27.5″ station vs. 29.84″ altimeter at 2,000 ft.
Why doesn't elevation change my DA number directly?
Because station pressure already encodes elevation. Two cars at the same physical elevation reading 27.0″ vs. 27.6″ will have different DAs — the math doesn't need elevation again. We display elevation here only as a sanity check and to show the delta between strip altitude and today's DA.
How accurate is the ET correction factor?
The shown factor is a rough rule-of-thumb for naturally-aspirated pump-gas cars — roughly 1% slower ET per 1000 ft of DA above the strip's physical elevation (and 1% quicker per 1000 ft below). It's deliberately calibrated against the strip's own standard-day baseline, so a textbook 59 °F / 29.92″ day at Vegas reads ~1.000×, not 1.08×. Real corrections vary by car, drive type, and tune. The in-app predictor uses a regression on YOUR runs instead of a generic factor and is typically within ±0.02 s after 20+ runs.
Can I bookmark a track's DA calculator?
Yes. Each link is of the form /density-altitude-calculator?elev=2188&track=Las+Vegas+Motor+Speedway. Bookmark or share it directly — the form pre-fills from the URL.
Where do live readings come from in the full app?
From the closest NOAA / National Weather Service station within ~60 mi, with Open-Meteo's gridded model as fallback outside the US. Or snap a photo of your Kestrel and let the AI read it. Every run logged in the app stores DA against the actual conditions at the moment of the pass.
Track DA per pass — that's where it pays off.
One calculation is a snapshot. A logbook tuned to live DA — auto-captured against every run — is the only honest way to compare passes day-to-day, track-to-track.