What Standard Atmosphere Pressure represents
The ISA tropospheric model starts at 1,013.25 hPa and 288.15 K, then applies a constant 6.5 K/km lapse rate under hydrostatic balance. This closed form returns the reference pressure at geopotential altitude.
Standard Atmosphere Pressure begins with geopotential altitude. Label every entry as observed, reduced, modeled, or assumed, and keep pressure type, vertical datum, timestamp, and reference atmosphere attached to the result.
Assumptions and stopping point
The page covers −500 to 11,000 m and does not implement stratospheric layers. Weather systems, temperature profiles, moisture, and latitude-dependent gravity produce departures from ISA.
Standard Atmosphere Pressure supplies transparent atmospheric arithmetic. It does not issue a forecast, identify hazardous weather, certify an instrument, define an official observing product, or authorize aviation, marine, field, or laboratory operations.
Hydrostatic and reference-atmosphere context
Several inputs to Standard Atmosphere Pressure assume hydrostatic balance, constant gravity, an ideal gas, or an ISA lapse rate. These are declared model choices, not observations of the current column.
Where profile data exist, compare the compact Standard Atmosphere Pressure estimate with a level-by-level calculation. Any disagreement helps reveal whether temperature structure, moisture, or the reference atmosphere controls the result.
Uncertainty and sensitivity
Test Standard Atmosphere Pressure with a credible low and high value for the least certain input, keeping the other entries unchanged. Report the resulting range in isa pressure rather than treating interface precision as measurement accuracy.
This Standard Atmosphere Pressure sensitivity range is not automatically a confidence interval. It omits correlations, representativeness error, vertical interpolation, sensor bias, and structural uncertainty in the chosen atmospheric model.
Pressure and height conventions
Pressure must be identified as absolute station pressure, reduced sea-level pressure, or altimeter setting before it enters Standard Atmosphere Pressure. Geometric elevation, geopotential height, pressure altitude, and density altitude likewise answer different questions.
For Standard Atmosphere Pressure, preserve the source datum and reference surface. Converting one vertical coordinate to another requires a stated gravity or standard-atmosphere model; renaming a column does not perform that conversion.
To extend the Standard Atmosphere Pressure record, use the related Barometric Pressure Change Rate Calculator with compatible inputs and conventions.
Temperature and moisture conventions
Absolute-temperature formulas inside Standard Atmosphere Pressure require kelvins even when the interface accepts degrees Celsius. Layer-mean virtual temperature is not interchangeable with a single surface thermometer reading.
When moisture affects Standard Atmosphere Pressure, distinguish specific humidity, mixing ratio, dew point, and virtual temperature. Each has a separate definition, and entering the same number under another label changes the physics.
Retaining an auditable record
Save raw Standard Atmosphere Pressure inputs, conversions, constants, formula version, unrounded output, rounded result, and any quality flags. Another reader should be able to repeat the calculation without guessing pressure type or altitude datum.
If an observation or assumption changes, make a dated Standard Atmosphere Pressure revision and preserve the earlier value. State whether the change corrects an error, updates a measurement, or explores a separate scenario.
Formula and unit route
The working relationship is P = 1013.25 × (1 − 2.25577×10⁻⁵z)^5.25588. Standard Atmosphere Pressure performs only the displayed conversion and does not retrieve a sounding, station report, forecast, or hidden atmospheric field.
Carry SI conversions explicitly through Standard Atmosphere Pressure: Celsius becomes kelvins where required, hectopascals become pascals for force equations, and kilometre scaling must be reconciled before interpreting a gradient.
Checked numerical example
At 2,000 m geopotential altitude, ISA pressure is approximately 794.95 hPa.
Reset restores this Standard Atmosphere Pressure example. Reproduce it independently with the stated constants before substituting measurements, and investigate discrepancies before trusting additional digits.
To extend the Standard Atmosphere Pressure record, use the related Virtual Temperature Calculator with compatible inputs and conventions.
Selecting compatible observations
Use geopotential altitude when strict consistency matters. If geometric elevation is entered directly, record that approximation and the vertical datum used.
For Standard Atmosphere Pressure, record location, sensor height, elevation datum, valid time, averaging interval, pressure reduction convention, temperature definition, moisture variable, and instrument resolution as applicable.
Interpreting ISA pressure
The answer is an ISA reference value for comparison and conversion. It does not describe the actual pressure at that altitude on a particular day.
Compare Standard Atmosphere Pressure outputs only when the source quantities share physical meaning and reference conventions. A numerically similar station pressure, sea-level pressure, and altimeter setting can still represent different quantities.
To extend the Standard Atmosphere Pressure record, use the related Hypsometric Thickness Calculator with compatible inputs and conventions.
To extend the Standard Atmosphere Pressure record, use the related Geostrophic Wind Calculator with compatible inputs and conventions.
Domain and boundary checks
At zero altitude, the formula returns exactly 1,013.25 hPa; pressure decreases monotonically with altitude in this domain.
Before accepting Standard Atmosphere Pressure, vary one input while holding the others fixed and predict the sign of change. This catches inverted pressure ratios, Celsius–kelvin errors, metres–feet mistakes, and endpoint reversal.
Common atmospheric calculation errors
Frequent Standard Atmosphere Pressure mistakes include treating hPa as Pa, using Celsius in a gas-law denominator, reversing upper and lower pressures, mixing feet with metres, or applying sea-level pressure to a local-density calculation.
Reject impossible Standard Atmosphere Pressure combinations rather than forcing an answer. Preserve genuine zero, missing data, trace values, and below-detection readings as different states. Check signs, logarithm arguments, denominator size, and the applicable vertical layer before using the output.
Questions about this pressure model
How should I round the answer?
Keep full precision inside Standard Atmosphere Pressure, then round no more finely than the least certain observation or model assumption supports.
When should I recalculate?
Recalculate Standard Atmosphere Pressure when the time, site, pressure type, elevation datum, parcel, layer, instrument value, or model assumption changes.
What does Standard Atmosphere Pressure calculate?
Standard Atmosphere Pressure calculates isa pressure from the displayed inputs and stated atmospheric relationship.