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What is considered low or high barometric pressure?

On the scale this site uses, sea-level barometric pressure below 29.68 inHg (1005 hPa) is low and above 30.12 inHg (1020 hPa) is high; anything in between is normal, and standard atmosphere sits at 29.92 inHg (1013.25 hPa). Other sources draw the lines a little differently — the most common alternative calls anything under 29.80 inHg (1009.1 hPa) low and anything over 30.20 inHg (1022.7 hPa) high.

The rest of this page covers why readings still confuse: the cut points are conventions, a barometer at altitude can read more than 5 inHg below the forecast, and for pressure sensitivity the site tracks change, not level.

The cut-offs on this site’s scale

Every live chart on the site is drawn over five fixed pressure zones. The thresholds are absolute sea-level values, identical for every city, so 1002 hPa means the same thing in Denver as it does in Miami.

The bands are anchored in hPa and converted at 1 hPa = 0.02953 inHg. If your app shows millibars, read them straight off the hPa column — 1 mb is exactly 1 hPa. For more on the middle band itself, see normal barometric pressure.

These are conventional reading points, not a standard — the methodology says so plainly. Cut points vary between sources; what matters is that this site uses the same ones for every city.

The other cut-offs you will see

The most common alternative is printed on many analog barometer dials and repeated across a number of pressure how-to pages: low below 29.80 inHg (1009.1 hPa), normal 29.80 to 30.20 inHg (1009.1–1022.7 hPa), high above 30.20 inHg (1022.7 hPa). Those pages share one lineage rather than being independent authorities, so treat it as a widespread convention, not a rule. Several also say pressure rarely goes above 30.50 inHg or below 29.40 inHg in inhabited places; “rarely” is the operative word, as the city records further down show.

The dial convention’s normal band runs higher at both ends, which leaves two strips where the same reading gets a different label:

• 29.68–29.80 inHg (1005–1009.1 hPa) — normal here, low on the dial. A reading of 29.75 inHg (1007.5 hPa) is the clearest example.
• 30.12–30.20 inHg (1020–1022.7 hPa) — high here, normal on the dial.

Neither label is wrong; when a source disagrees with this site, you are almost always in one of these strips.

Is my reading high or low? A lookup table

Most people arrive with a number from an app, a watch or a wall barometer. Here is 29.00–31.00 inHg under both conventions, plus a few commonly searched values. All are sea-level pressure; for a raw station reading at altitude, see the station-pressure section first.

29.84 inHg is not low on either scale; 29.92 inHg is the textbook middle; 28.90 inHg is low by any convention and very low on this one.

Is 30.02 inHg high? No — it is normal, 0.10 inHg below where this site’s high zone begins, and normal on the dial convention too.

What causes high and low barometric pressure?

The zones are labels for a number, but each band tends to travel with a particular kind of weather. The site’s methodology gives the typical association for each:

• Very low (below 29.38 inHg / 995 hPa) — a deep low-pressure system; storm conditions.
• Low (29.38–29.68 inHg) — unsettled; cloud and precipitation more likely.
• High (30.12–30.42 inHg) — settled, drier, often clear.
• Very high (above 30.42 inHg / 1030 hPa) — a strong anticyclone; cold, stable air masses.

Read these as typical associations, not guarantees: a low reading makes cloud and rain more likely without promising them, and a single number says nothing about where the weather is heading. For how lows, highs and fronts move the barometer as they pass, see falling and rising barometric pressure.

How far high and low actually go in US cities

These figures come from this site’s ten-year dataset — Open-Meteo ERA5 hourly reanalysis, 2015–2024, sea-level-reduced. “Typical range” is the 5th to 95th percentile of all hours: 90% of the time, pressure was inside it.

inHg, with hPa in parentheses. Sea-level-reduced ERA5 reanalysis, 2015–2024.

Miami is the steadiest barometer of the 50 cities (standard deviation 0.11 inHg, or 3.57 hPa, the lowest in the set). Its typical range sits mostly inside the normal band, so a reading of 29.68 inHg there is genuinely unusual.

Phoenix has one of the lowest mean pressures of the 50, 29.89 inHg (1012.3 hPa), yet it never dropped into very low: its record low of 29.43 inHg (996.7 hPa) only just reaches into low.

Boston and Salt Lake City show the extremes. Boston’s record low of 28.66 inHg (970.7 hPa), on February 7, 2020, is deep in very-low territory and well under the 29.40 inHg that dial-convention pages describe as rare. Salt Lake City has the most variable pressure in the set — standard deviation 0.26 inHg (8.64 hPa), first of 50 — and a top-5% threshold of 30.49 inHg (1032.6 hPa), meaning very-high readings show up there for more than 5% of hours. Its record of 31.08 inHg (1052.4 hPa) is far above 30.50.

The lines are fixed, but how often you cross them depends heavily on where you live. Each city page shows that city’s own percentiles and records.

Why your barometer reads far lower than the forecast

If your device shows something like 24.7 inHg and every number on this page starts with 29 or 30, you are almost certainly looking at station pressure: the raw reading at your elevation. Weather reports and every band above use sea-level-reduced pressure, adjusted to what it would be at sea level so that cities can be compared.

The gap grows with altitude:

In Denver the difference averages about 5.23 inHg (177 hPa); in Colorado Springs, the highest of the site’s 50 cities, about 5.85 inHg (198 hPa). Even Phoenix, at 333 m, averages a station reading of 28.77 inHg — “very low” on any sea-level scale in perfectly ordinary weather. Check which kind of reading your device shows before comparing it to any table; each city page lists mean station pressure next to the sea-level figures for exactly this reason.

One more caveat cuts the other way: reducing pressure to sea level at high elevation amplifies temperature-driven variation, which is part of why Front Range cities rank so high for volatility — Colorado Springs has the most big-swing days of the 50, 171.6 a year. Those sea-level swings are real, but somewhat inflated.

Level or change: which matters more?

Which is worse, high or low? Neither level is bad in itself, and level is not what the site watches for pressure sensitivity. A falling barometer is the direction most often described in pressure-sensitivity reports, so each city page’s outlook is built on 24-hour change — a swing day means a change of at least 0.18 inHg (6 hPa), a big-swing day 0.30 inHg (10 hPa) or more. Those are conventional bins in the pressure-and-headache literature, not clinically validated thresholds.

Level and change are separate things. Miami and Boston both average about 30 inHg, yet Miami’s top 5% of 24-hour changes reach only 0.14 inHg (4.6 hPa) while Boston’s reach 0.54 inHg (18.2 hPa) — and Boston’s sharpest single 24-hour fall, 1.52 inHg (51.5 hPa), is the largest of the 50 cities. For what a moving barometer means for the weather, see falling and rising barometric pressure; for what is and is not known about pressure and symptoms, see barometric pressure effects on the body.

On the health question itself, the site’s position is association, not causation: the effect sizes are modest, the findings are mixed, and individual sensitivity varies widely.

Association only. Pressure zones and swing-day counts describe the weather, not you. Pressure change is associated with symptoms in some pressure-sensitive people, but nothing on this page is a prediction of symptoms, a diagnosis, or medical advice. If headache or migraine is affecting your life, talk to a clinician.

Reading your own number

• Check the type first. A reading near 24–29 inHg at elevation is probably station pressure.
• Then the band. Under 29.68 inHg (1005 hPa) is low and over 30.12 inHg (1020 hPa) is high here; a disagreeing source usually means you are in one of the two strips.
• Then the context. The same reading is routine in one city and rare in another — see all 50 city pages, or check any US location.

All 50 city pages · Check any US location · Methodology