A wide view of rolling green hills under a clear blue sky, with a band of grey rain cloud gathering far off on the horizon
AI-generated image, not a photograph of a real person or place.
doodlepressure

WHAT THE WEATHER CHART SAYS

The weight
of the sky.

1013 mb standard at sea level

  • Highs settle
  • Lows stir things up
  • Tight lines, strong wind
  • Three rules for any weather chart

Air presses on everything, all the time.

Weather forecasters measure that push in millibars and draw it as lines on a chart. Read those lines and you can tell a calm, frosty high from a wet and windy low.

Updated

Read a chart

THE SHORT ANSWER

High means settled,
low means unsettled.

Air pressure is the force of the atmosphere on the ground.
Forecasters compare one place with its surroundings.

THE NUMBER

What a millibar is

Pressure is measured in hectopascals or millibars, and 1 hPa is the same as 1 mb. Standard sea-level pressure is 1013 hPa.

See the numbers

THE CHART

Highs and lows

Sinking air makes high pressure and settled weather. Rising air makes low pressure and unsettled weather, with cloud and rain.

Read a chart

YOUR EARS

Why ears pop

When a plane climbs or descends, pressure changes fast and a small tube in the ear has to catch up. Swallowing or yawning helps.

What helps

A QUICK CHART CHECK

What is the pressure
doing today?

Pick a situation from a weather chart to see the weather the Met Office says it usually brings. The bar shows how unsettled it tends to be.

Chart check

Choose a situation
A high in summerFine and warm

Fine, warm weather with long sunny days and dry spells. Winds around a high tend to be light.

A high in winterCold and dry

Cold, dry days with light winds, and the chance of severe frosts at night.

A low in summerRain

Prolonged rainfall, sometimes heavy enough to cause flooding.

A low in winterStormy or wintry

Stormy or wintry conditions often occur when low pressure sits over the country in winter.

Isobars packed closeStrong winds

Closely spaced isobars mean strong winds. Widely spaced ones suggest lighter winds.

Source: Met Office, High and low pressure, and How to read a synoptic weather chart.

Based on Met Office guidance on high and low pressure and on reading synoptic charts. General patterns, not a forecast.

TWO NUMBERS WORTH KNOWING

Most of the air
is close to the ground.

One number for normal pressure,
one for how quickly it thins with height.

1013 hPa

Standard sea-level pressure

The Met Office gives standard sea-level pressure as 1013 hPa. NOAA puts it at 1013.25 mb, or 29.92 inches of mercury on older barometers.

SEA LEVEL · MET OFFICE

5.6 km

Half the air sits below about

NOAA says about half of the atmosphere's air molecules lie below roughly 18,000 feet, or 5.6 km. Pressure falls with height because the air gets thinner.

ALTITUDE · NOAA

Weather stations sit at different heights, so their readings are adjusted to sea-level values before they go on a chart. That is how a hilltop and a harbour can be compared.

WHEN YOUR EARS POP

Help your ears
catch up.

A passenger seen from behind looking out of an aeroplane window at clouds below during descent
AI-generated image, not a photograph of a real person or place.

The eustachian tube links the middle ear to the back of the nose and throat and keeps pressure even. On take-off and landing it can lag behind. Mayo Clinic suggests:

  1. Swallow or yawn

    Do it during take-off and landing. Sucking a sweet or chewing gum makes you swallow more.

  2. Try a gentle blow

    Pinch your nostrils, keep your mouth closed and blow gently, as if blowing your nose. Repeat during descent.

  3. Stay awake for landing

    Sleeping through take-off or landing raises the risk, because you are not swallowing or yawning.

  4. Help babies swallow

    Give a bottle or dummy during descent, with the child sitting upright while drinking.

UK EXTREMES

From 925 to
1053 millibars.

A brass aneroid barometer with a white dial hanging on a hallway wall in soft morning light
AI-generated image, not a photograph of a real person or place.

The Met Office lists 925.6 mb at Ochtertyre, Perthshire, on 26 January 1884 as one of the UK's lowest January pressures. As recently as 24 January 2025, Magilligan in Northern Ireland recorded 948.1 mb.

At the other end, Aberdeen recorded 1053.6 mb on 31 January 1902, Falmouth 1053.1 mb in 1905 and Mumbles in Wales 1050.5 mb in 2020. Around a high like that, winds are light and blow clockwise.

Questions

Questions people ask

What is a millibar?

A unit of air pressure. One millibar is the same as one hectopascal, which is 100 pascals. Forecasters use millibars or hectopascals on weather charts.

What is normal air pressure?

The Met Office gives standard sea-level pressure as 1013 hPa. Highs and lows are defined by comparing a place with its surroundings, not by one fixed number.

What are the lines on a weather chart?

They are isobars, lines joining places with equal sea-level pressure. The closer together they are, the stronger the wind.

Which way does wind blow around a low?

In the northern hemisphere, air circulates anticlockwise around low pressure and clockwise around high pressure, moving from higher to lower pressure.

Why do my ears hurt on a plane?

Pressure changes quickly as a plane climbs and descends, and the eustachian tube may not equalise fast enough. Mayo Clinic advises seeing a doctor if symptoms are severe or last more than a few days.

Sources

Where the facts come from

  1. Met Office: High and low pressure
  2. Met Office: How to read a synoptic weather chart
  3. Met Office blog: January weather extremes, records from past events
  4. NOAA JetStream: Air pressure
  5. Mayo Clinic: Airplane ear, symptoms and causes

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