Adiabatic Lapse Rate Calculator
How fast lifted air cools — the dry rate is gravity over heat capacity, which is why the pilot rule of 3 C per 1000 ft is the physics rounded.
This is a parcel lifted without exchanging heat with its surroundings, which is an idealisation — real air mixes, and a real sounding wanders. The dry figure is exact for the idealisation; the saturated ones are representative rather than fixed. Nothing is uploaded.
The dry rate is not measured — it is gravity over a heat capacity
Lift dry air without letting heat in or out and it expands against falling pressure, spending its own energy to do the work. How fast it cools per metre is simply g / cp — 9.80665 over 1005 — 9.76 °C per kilometre. No weather enters it, which is why the number is the same over an ocean and a desert.
| Rate | Per km | Per 1000 ft | 20°C becomes |
|---|---|---|---|
| Dry adiabatic — derived from g/cp | 9.76 °C | 2.97 °C | 10.2 °C at 1 km |
| Saturated, typical | 5.00 °C | 1.52 °C | 15.0 °C at 1 km |
| Saturated, warm and very moist | 4.00 °C | 1.22 °C | 16.0 °C at 1 km |
| Saturated, cold and dry | 8.00 °C | 2.44 °C | 12.0 °C at 1 km |
| Standard atmosphere average | 6.50 °C | 1.98 °C | 13.5 °C at 1 km |
Which is where the pilot's rule comes from: 2.97°C per thousand feet, taught as three. The rule of thumb is the physics rounded to one figure, and it is within one percent. The saturated rate is a different animal — roughly half, because condensation gives heat back, and genuinely variable because it depends how much water there is to condense.
So a lifted parcel cools in a straight line
Exactly linear, because the rate is a constant. A 20°C parcel lifted dry reaches freezing just over two kilometres up. The same parcel saturated is still above freezing at three, and the gap between the two widens the whole way — which is most of why cloudy air and clear air behave so differently above you.
| Height | In feet | Dry parcel | Saturated parcel |
|---|---|---|---|
| 0 m | 0 ft | 20.0 °C | 20.0 °C |
| 500 m | 1640 ft | 15.1 °C | 17.5 °C |
| 1000 m | 3281 ft | 10.2 °C | 15.0 °C |
| 2000 m | 6562 ft | 0.5 °C | 10.0 °C |
| 3000 m | 9843 ft | -9.3 °C | 5.0 °C |
| 5000 m | 16404 ft | -28.8 °C | -5.0 °C |
The standard atmosphere's 6.5°C per kilometre sits between the two, which is the honest summary of real air: sometimes dry, sometimes saturated, and on average somewhere in between. It is an average of behaviour rather than a rate anything actually follows.
How to use
- Enter the surface temperature.
- Enter how far the parcel is lifted.
- Set the lapse rate, or leave the dry adiabatic value.
- Read the temperature aloft and the freezing level.
Frequently asked questions
What is the dry adiabatic lapse rate?
Gravity divided by the specific heat of air — 9.80665 over 1005, which is 9.76 C per kilometre. It is derived rather than measured, so it is the same over an ocean as over a desert.
Why is it not a weather measurement?
Because no weather enters the derivation. A parcel lifted without exchanging heat expands against falling pressure and spends its own energy doing the work, and how fast that cools it depends only on gravity and how much heat air holds per degree.
Where does the 3 degrees per 1000 feet rule come from?
From exactly this. The dry rate works out at 2.97 C per thousand feet, and the rule is that number rounded to one figure — within one percent of the physics rather than a separate approximation.
Why is the saturated rate different?
Because condensation releases latent heat and gives some of the cooling back. It roughly halves the rate, to around 5 C per kilometre, and unlike the dry rate it is genuinely variable — it depends how much water there is to condense.
Which rate should I use?
The dry one until the parcel saturates, and the saturated one above that. The dry rate is exact for the idealisation; the saturated figure here is representative and is an input so you can set your own.
What is the standard atmosphere rate?
6.5 C per kilometre, which sits between the two. That is an average of real behaviour rather than a rate anything actually follows — real air is sometimes dry, sometimes saturated, and on average somewhere in between.
Where does a lifted parcel reach freezing?
Divide the surface temperature by the lapse rate. A 20 C parcel lifted dry passes freezing just over two kilometres up; the same parcel saturated is still above freezing at three, and the gap widens the whole way.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.