CAPE and CIN Calculator
Calculate Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) from parcel and environmental temperatures at multiple pressure levels.
About this calculator
CAPE and CIN measure the two opposing forces that decide whether a rising air parcel actually becomes a thunderstorm. This calculator breaks the atmosphere into three layers — surface to 850 mb, 850 to 700 mb, and 700 to 500 mb — and for each one computes buoyant energy using Rd·(Tp − Te)·ln(p1/p2), where Rd is the gas constant for dry air (287.04 J/(kg·K)) and the temperature difference is the average of the parcel's and environment's temperatures across the layer's two boundaries. When the lifted parcel is warmer than its surroundings within the layer bounded by your LFC (Level of Free Convection) and EL (Equilibrium Level) pressures, that layer's energy adds to CAPE — fuel for an updraft. When the parcel is colder than the environment, that energy subtracts as CIN — an energy barrier, or "cap," the parcel must be forced through before free convection can begin.
From total CAPE, the calculator estimates a theoretical maximum updraft speed using w = √(2 × CAPE), a simplification that assumes all buoyant energy converts perfectly into vertical motion with no entrainment or precipitation drag — real updrafts run slower. Storm potential and CIN inhibition labels are standard forecasting thresholds (2500+ J/kg CAPE for violent storms, 200+ J/kg CIN for a strong cap). This is a simplified three-layer approximation of what a full Skew-T sounding analysis does continuously through hundreds of levels, so treat the numbers as directionally useful rather than as a substitute for real sounding data — the coarser your pressure-level spacing, the more energy detail gets averaged away.
Inputs
Results
CAPE
594 J/kg
CIN
0 J/kg
How to Use This Calculator
- Enter temperature (°C) for the air parcel and environment at each pressure level: surface, 850 mb, 700 mb, and 500 mb.
- Set LFC Pressure (mb) — the Level of Free Convection where the parcel becomes buoyant.
- Set EL Pressure (mb) — the Equilibrium Level where the parcel returns to neutral buoyancy.
- Review CAPE (J/kg): below 1000 = weak instability, 1000–2500 = moderate, 2500–3500 = large, 3500+ = extreme.
- Check CIN (J/kg) — values above 200 indicate a strong cap that may suppress storms even with high CAPE.
How the result changes with Parcel Temp (850 mb)
| Parcel Temp (850 mb) | CAPE | CIN |
|---|---|---|
| 9 | 338 J/kg | 205 J/kg |
| 14 | 389 J/kg | 0 J/kg |
| 27 | 1,055 J/kg | 0 J/kg |
| 30 | 1,208 J/kg | 0 J/kg |
What each input means
- Parcel Temp (Surface)
- Lifted parcel temperature at the surface level in °C.
- Environment Temp (Surface)
- Observed environmental temperature at the surface in °C.
- Parcel Temp (850 mb)
- Lifted parcel temperature at 850 mb (~1,500 m) in °C.
- Environment Temp (850 mb)
- Environmental temperature at 850 mb from sounding data in °C.
- Parcel Temp (700 mb)
- Lifted parcel temperature at 700 mb (~3,000 m) in °C.
- Environment Temp (700 mb)
- Environmental temperature at 700 mb from sounding data in °C.
- Parcel Temp (500 mb)
- Lifted parcel temperature at 500 mb (~5,500 m) in °C.
- Environment Temp (500 mb)
- Environmental temperature at 500 mb from sounding data in °C.
- LFC Pressure
- Level of Free Convection in mb — the altitude where the parcel becomes buoyant.
- Equilibrium Level
- Equilibrium Level in mb — the altitude where parcel temperature equals environment temperature.
What each result means
- CAPE
- Total convective energy available for thunderstorm updrafts.
- CIN
- Convective inhibition — energy barrier that must be overcome for storm initiation.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersParcel Temp (Surface) = 30, Environment Temp (Surface) = 28, Parcel Temp (850 mb) = 18, Environment Temp (850 mb) = 15 = 10 input(s) provided
- Calculate CAPECAPE = energy594 = 594
- Calculate CINCIN = Math0 = 0
- Calculate Max Updraft SpeedMax Updraft Speed34.5 = 34.5
- Calculate Storm PotentialStorm PotentialSlight — Weak Storms Possible = Slight — Weak Storms Possible
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the calculator only use three atmospheric layers instead of a full sounding?
It computes buoyant energy across surface-to-850mb, 850-to-700mb, and 700-to-500mb because those are the pressure levels this calculator's inputs collect. A real forecast sounding integrates buoyancy continuously through dozens of levels, so this three-layer version necessarily averages away finer detail within each layer.
How does the calculator decide whether a layer's energy counts toward CAPE or CIN?
A layer adds to CAPE only when its midpoint pressure falls between your LFC and EL inputs and the parcel is warmer than the environment (positive energy) there. Any layer where the parcel is colder than the environment — negative energy — adds to CIN instead, regardless of where it falls relative to LFC and EL.
Why might the Max Updraft Speed be higher than what a real storm would produce?
It's computed as the square root of 2 times total CAPE, which assumes every joule of buoyant energy converts perfectly into vertical motion. Real updrafts lose energy to entrainment of drier surrounding air and to the drag of suspended precipitation, so actual updraft speeds typically run below this theoretical maximum.
Why do I need to enter LFC and EL pressures myself instead of the calculator finding them?
The Level of Free Convection and Equilibrium Level mark the pressure band where a lifted parcel is actually buoyant, and this simplified three-layer model uses them directly to decide which layers count toward CAPE rather than deriving them from a continuous profile. Getting these two values right from your sounding data is what keeps the CAPE/CIN split meaningful.
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