A2992 vs Q1013: The Two Altimeter Settings, Decoded

A2992 vs Q1013 is not a contest between two pressures. It is the same pressure written in two units. The A-group is inches of mercury and the Q-group is hectopascals, and which one you get depends entirely on where the station is.

That sounds harmless. It is the single most common unit error in international flying, and it is worth ten minutes now to never make it.

What A2992 vs Q1013 actually says

An A-group is four digits after the letter A, with the decimal point removed. A2992 means 29.92 inches of mercury. A3015 means 30.15 inches. The point always sits after the second digit, so you can read it at a glance.

A Q-group is four digits after the letter Q, in whole hectopascals. Q1013 means 1013 hectopascals. There is no decimal point to put back. What you see is the number you dial.

Both are QNH. That is the setting that makes your altimeter read field elevation when you are on the ground. Neither is a different kind of pressure. They are a different kind of writing.

Which one you will see, and where

The United States uses inches. So do Canada and Japan. Almost everybody else uses hectopascals, including all of Europe, most of Asia, and Australia.

You can predict it from the station identifier most of the time. A K-prefix field reports inches. An E, L or Y prefix field reports hectopascals. It is a rule of thumb rather than a law, so read the group rather than assume it.

Russia and a handful of neighbours add a third option. They report QFE, the pressure at the field surface rather than at sea level, which makes the altimeter read zero on the ground. That is a different setting again, not a different unit for the same one.

How to convert between them

One inch of mercury is 33.8639 hectopascals. To go from inches to hectopascals, multiply. To go the other way, divide.

Two anchors are worth memorising. Standard pressure is 29.92 inches, which is 1013.2 hectopascals. And roughly one hundredth of an inch is one third of a hectopascal, so a thirty hectopascal spread is about nine tenths of an inch.

For a rough field check, subtract 1000 from the hectopascals, divide by 34, and add that to 29.53. It is close enough to catch a gross error, which is all a mental check needs to do.

Where the group sits in the report

Both groups come near the end of the body, straight after the temperature and dew point. That position is fixed, so you can find the setting without reading anything before it.

A US report runs wind, visibility, weather, cloud, then 06/04, then A2990. An international report runs the same order and finishes 06/04 Q1013. Same slot, different letter.

After the altimeter comes RMK and the remarks. US stations often repeat the pressure there in a different form. SLP125 is sea-level pressure, 1012.5 hectopascals, and it is not the altimeter setting. It is a meteorological number, useful for tracking systems and wrong for your altimeter.

That catches people who spot a familiar four digit value in the remarks and dial it. If it sits after RMK, it is not your setting.

Why reading one as the other is a hazard

An altimeter set wrong reads the wrong height, and the error is about 1000 feet per inch of mercury. That is roughly 30 feet per hectopascal.

Picture a low pressure day in Europe. The field reports Q0985. A pilot used to inches dials 29.85 instead. The gap between 985 hectopascals and 29.85 inches, which is about 1011 hectopascals, is 26 hectopascals. The altimeter now reads about 780 feet high, so the aircraft flies 780 feet low.

That is the whole hazard in one sentence. On approach, in cloud, it is the difference between a normal arrival and a very short one.

The transition altitude trap

Units are only half the problem abroad. The other half is when you stop using QNH at all.

In the United States everybody switches to the standard 29.92 at 18,000 feet. That number is the same countrywide, so it becomes automatic. Across much of Europe the transition altitude is far lower and it varies by airport, sometimes 3000 feet, sometimes 5000, sometimes 6000.

So a crew trained on a fixed 18,000 arrives somewhere the switch happens minutes after takeoff. Miss it and you climb on a local setting when everyone around you is on standard. Read the transition altitude off the plate before you need it.

Verdict on A2992 vs Q1013

Read the letter before the number, every time. The letter is the unit and the number means nothing without it.

If you fly only inside the United States you will see A-groups and nothing else, and this stays trivia. The moment you cross a boundary it stops being trivia. Get in the habit of saying the unit out loud when you set it, because the number alone is what gets people.

Last updated August 29, 2026