A2992 Is Pressure, Not Temperature

Near the end of a METAR you reach a token like A2992, and at first glance it reads like a four-digit number that could be almost anything. It is not a temperature: A2992 is the altimeter setting of 29.92 inches of mercury, the value pilots set in the Kollsman window, not the temperature. That single token tells your altimeter how to translate the current air pressure into an altitude, and wxdecoder.com spells it out so there is no second-guessing. Once you know where it sits in the report and what the prefix means, it decodes the same way every time.

This guide covers the US A form in inches of mercury, the ICAO Q form in hectopascals, why both are sea-level settings tied to the Kollsman window, and what goes wrong when the setting is off. It is part of the METAR field guide.

Where pressure sits in the report

A METAR runs through its groups in a fixed order: station, time, wind, visibility, weather, clouds, then temperature and dewpoint, and finally the pressure group before any remarks. That ordering is the first defense against confusion. The temperature lives one group earlier as a slash-separated pair like 02/M01, while the pressure stands alone with a letter prefix. If you are unsure which is which, the temperature and dewpoint group explains the M minus prefix and the slash format in detail.

So in a tail that ends 02/M01 A2992, the 02/M01 is 2C over -1C and the A2992 is the pressure. Two adjacent groups, two completely different quantities.

The US form: A for inches of mercury

In the United States the altimeter setting is reported in inches of mercury with an A prefix and four digits, with the decimal point implied two places in:

A2992    =  29.92 inHg
A3015    =  30.15 inHg
A2978    =  29.78 inHg

A2992 is 29.92 inches of mercury, the standard sea-level pressure and a number worth memorizing because it is the value used as a reference at and above the transition altitude. Read the four digits, drop a decimal point after the second one, and you have the setting in inches.

The ICAO form: Q for hectopascals

Outside the US, most of the world reports the same setting in hectopascals with a Q prefix. This is the QNH:

Q1013    =  1013 hPa
Q0998    =  998 hPa
Q1024    =  1024 hPa

Q1013 is 1013 hectopascals, the metric near-equivalent of 29.92 inches. The four digits are simply the pressure in whole hectopascals, no decimal involved. A METAR uses one form or the other depending on the issuing country, so seeing a Q group tells you the station follows ICAO conventions. Either way, when you paste the report into the decoder it converts and labels the value for you.

Both feed the Kollsman window

The A and Q values are not abstract weather trivia. They are the number a pilot dials into the small adjustment window on the face of the altimeter, the Kollsman window. Both forms express the same physical thing: the local sea-level pressure setting, often called the altimeter setting or QNH.

When you turn the knob until the Kollsman window shows the reported setting, the altimeter is calibrated so that on the ground it reads the published field elevation. Set A2992 at an airport whose elevation is 600 feet and a correctly working altimeter reads about 600 feet on the ramp. That is the whole point of broadcasting the value: every aircraft at the field references the same pressure, so everyone's altimeter agrees.

Why a wrong setting misreads altitude

The altimeter is a pressure instrument pretending to be a height instrument. It senses air pressure and converts it to an altitude using whatever number sits in the Kollsman window, so the reading is only as correct as the setting. Pressure falls as you climb, so the instrument assumes lower pressure means higher altitude.

That dependence is why the setting matters operationally. If the actual pressure has dropped since you last set the altimeter and you do not update it, the instrument reads higher than you truly are, and you can be lower than the dial suggests on an approach. The old memory aid is "high to low, look out below." Updating the Kollsman window with each station's current A or Q value as you fly keeps the indicated altitude honest. This is situational-awareness information from wxdecoder, not an official briefing, but the rule of thumb is durable: stale pressure means an unreliable altitude.

A more precise pressure in the remarks

The A or Q group is rounded for setting an altimeter, but US reports often carry a finer sea-level pressure value in the remarks as an SLP group. SLP132 decodes to 1013.2 hPa and SLP984 to 998.4 hPa, giving a tenth-of-a-hectopascal reading that the rounded altimeter group cannot. If you want that extra precision and the rest of the coded remarks, the remarks guide walks through SLP and the other RMK groups.

Worked examples

...10SM FEW250 02/M01 A2992 Temperature 2C, dewpoint -1C, altimeter 29.92 inches of mercury. The pressure group is the last token before any remarks.

...9999 SCT040 15/09 Q1013 An ICAO-style report: visibility 10 km or more, and a QNH of 1013 hectopascals to set in the Kollsman window.

...A3015 RMK AO2 SLP218 Altimeter 30.15 inches for the cockpit, with a more precise sea-level pressure of 1021.8 hPa tucked into the remarks.

Decode the pressure group instantly

The pattern never changes: an A plus four digits is inches of mercury with an implied decimal, a Q plus four digits is whole hectopascals, and both are the sea-level setting for your altimeter rather than a temperature. When you would rather have it read for you, paste the raw report into wxdecoder and the pressure group, units and all, comes back as a labeled plain-English line.

Last updated June 29, 2026