What is the air pressure at 1,000 metres altitude?

At 1,000 metres above sea level, the standard atmospheric pressure is approximately 89,875 Pa (898.75 hPa or 89.88 kPa). This is about 88.7% of the sea-level standard pressure of 101,325 Pa. The reduction follows the International Standard Atmosphere barometric formula: P = 101325 x (1 - 0.0000225577 x h)^5.25588, where h is altitude in metres.

Why does air pressure decrease with altitude?

Air pressure at any point equals the weight of the air column above it. As you rise in altitude, there is less air above you, so the column weighs less and pressure is lower. In the troposphere (roughly 0 to 11 km), pressure drops by about 12 Pa for every 1 metre of altitude gained near sea level, though the rate slows as altitude increases. Temperature also drops with altitude (at a lapse rate of about 6.5 degrees Celsius per 1,000 m), which affects air density and hence pressure.

What is the difference between the troposphere and stratosphere pressure formulas?

In the troposphere (0 to 11,000 m), temperature decreases at a constant lapse rate of 6.5 K per 1,000 m, so the barometric formula uses a power law: P = 101325 x (1 - 2.25577e-5 x h)^5.25588. In the lower stratosphere (11,000 to 20,000 m), temperature is constant at -56.5 degrees Celsius (216.65 K), so pressure decreases exponentially: P = 22632.1 x exp(-0.0001577 x (h - 11000)). These are the standard ISA (International Standard Atmosphere) formulas used by aviation, meteorology, and engineering.

Air Pressure at Altitude Calculator

This calculator works out standard atmospheric pressure at any altitude using the barometric formula from the International Standard Atmosphere (ISA), the reference model used in aviation, meteorology and engineering. Pressure falls as you climb because there is less air above you pressing down, and this tool shows exactly how much it drops at a given height. You enter an altitude in metres, feet or kilometres, either typing a figure or picking a preset from sea level up to Mt Everest's summit, and you can adjust the reference sea-level pressure and temperature to model non-standard starting conditions. It returns pressure at that altitude in five units at once - pascals, hectopascals, kilopascals, atmospheres and millimetres of mercury - plus the temperature and atmospheric layer at that height (troposphere up to 11,000 m or lower stratosphere from 11,000 to 20,000 m), and a comparison table showing pressure across a range of key altitudes side by side. It covers altitudes from sea level to 20,000 m, applying the correct formula for whichever layer your figure falls into. Use it to understand how pressure changes with height for flying, hiking, weather work or study, and remember these are standard, theoretical figures rather than a live weather reading: real-world pressure varies with weather systems, season and latitude, so for aviation, medical or safety-critical decisions always rely on calibrated instruments rather than this indicative calculation.

Calculate.co.nz is proud to be partnered with Health Based Building, a leader in sustainable and health-conscious building innovation. With over a century of experience, they develop high-performance systems like Foreverbreathe Specification, Magnum Board, and Foreverbreathe Paints to support energy-efficient, non-toxic living environments. Their commitment to healthier homes aligns with our belief that informed choices lead to better outcomes for Kiwi households.

Calculate.co.nz partner: Health Based Building

Updated International Standard Atmosphere (ICAO Doc 7488). Covers troposphere (0 to 11,000 m) and lower stratosphere (11,000 to 20,000 m).

1. Altitude Input

Altitude unit

Altitude (m above sea level)

Common altitudes

2. Reference Conditions

Atmospheric model

Sea-level pressure (Pa)

Sea-level temperature (K)

Atmospheric Pressure at Altitude

Pressure (hPa)
898.75
Hectopascals

Pressure (Pa)

89,875

Pascals

Pressure (kPa)

89.875

Kilopascals

Pressure (atm)

0.8870

Atmospheres

Pressure (mmHg)

674.1

Millimetres mercury

Pressure at Key Altitudes

Altitude	Pressure (hPa)	Pressure (Pa)	% of Sea Level	Temp (K)	Layer

Calculation Details

Altitude input1,000 m

Altitude (m)1,000.0 m

Atmospheric layerTroposphere (0 to 11,000 m)

Temperature at altitude281.65 K (8.5 °C)

Sea-level pressure (P0)101,325 Pa

Pressure at altitude89,874.8 Pa (898.75 hPa)

Worked Example

Formula (troposphere)P = P0 x (1 - L x h / T0)^(g x M / (R x L))

P0 (sea-level pressure)101,325 Pa

T0 (sea-level temperature)288.15 K

L (lapse rate)0.0065 K/m

Exponent (gM/RL)5.25588

At h = 1,000 m101325 x (1 - 2.25577e-5 x 1000)^5.25588

Result89,875 Pa (898.75 hPa)

Result: At 1,000 m (1,000 m), standard atmospheric pressure is 898.75 hPa (89,875 Pa), which is 88.7% of sea-level pressure. Temperature: 8.5 °C under ISA conditions.

How to Calculate Air Pressure at Altitude

Atmospheric pressure decreases with altitude because there is less air above any given point to exert its weight. The standard method for calculating pressure at altitude is the barometric formula from the International Standard Atmosphere (ISA), defined by ICAO (International Civil Aviation Organisation).

The Barometric Formula

The ISA divides the atmosphere into layers. For everyday altitudes up to 11,000 metres (the troposphere), the formula is:

P = P0 x (1 - L x h / T0)^(g x M / (R x L))

Where:

P = pressure at altitude h (Pa)
P0 = sea-level standard pressure = 101,325 Pa
L = temperature lapse rate = 0.0065 K/m
h = altitude above sea level (m)
T0 = sea-level standard temperature = 288.15 K (15 degrees Celsius)
g = gravitational acceleration = 9.80665 m/s squared
M = molar mass of dry air = 0.0289644 kg/mol
R = universal gas constant = 8.31446 J/(mol K)

The exponent g x M / (R x L) evaluates to approximately 5.25588. The formula simplifies to:

P = 101325 x (1 - 0.0000225577 x h)^5.25588

Lower Stratosphere (11,000 to 20,000 m)

Above 11,000 m, the temperature is constant at 216.65 K (-56.5 degrees Celsius). Pressure decreases exponentially:

P = 22632.1 x exp(-0.0001577 x (h - 11000))

Where 22,632.1 Pa is the pressure at the tropopause (11,000 m) under ISA conditions.

Pressure at Common Altitudes

Location / Altitude	Altitude (m)	Pressure (hPa)	% of Sea Level
Sea level	0	1013.25	100%
Queenstown, NZ (approx)	310	976	96.3%
1,000 m	1,000	898.75	88.7%
Aoraki / Mt Cook	3,724	640	63.2%
Everest Base Camp	5,364	514	50.8%
Mt Everest summit	8,849	315	31.1%
Airliner cruise (35,000 ft)	10,668	237	23.4%
Tropopause	11,000	226.3	22.3%

Why It Matters

Air pressure at altitude affects many practical situations. Pilots use pressure altitude to set altimeters and calculate aircraft performance. Hikers and climbers need to understand that lower pressure means less available oxygen, which becomes significant above about 3,000 m. Meteorologists use the pressure-altitude relationship to convert between station pressure and sea-level pressure on weather maps. Engineers design pressurised aircraft cabins and equipment to maintain safe pressure levels at cruising altitude. Cooks at altitude often need to adjust recipes because water boils at lower temperatures when pressure is reduced.

Real vs Standard Atmosphere

The ISA formula gives the standard or theoretical pressure. Actual atmospheric pressure varies with weather, season, and latitude. For accurate real-world measurements, you need a barometer. The ISA model is used as a reference baseline for aviation, engineering design, and instrument calibration rather than as a live weather forecast.

Related Calculators

Sources and method: International Standard Atmosphere (ISA) as defined by ICAO Doc 7488. US Standard Atmosphere 1976. Barometric formula: P = P0 x (1 - L x h / T0)^(g x M / (R x L)) for the troposphere (0 to 11,000 m); P = 22632.1 x exp(-0.0001577 x (h - 11000)) for the lower stratosphere (11,000 to 20,000 m).

This calculator uses the International Standard Atmosphere model, which gives standard conditions. Actual atmospheric pressure varies with weather and season. For aviation, engineering, or medical applications always use calibrated instruments and consult relevant regulations and standards.