How to Read an Altimeter: A Practical Guide

An altimeter shows an estimate of your altitude, usually above mean sea level. Knowing how to read one helps you interpret aircraft instruments, hiking or navigation devices, and some watches. The exact method depends on the type: a traditional dial, an electronic display, or a specialized instrument such as a skydiving altimeter. Before using it for navigation or flight, learn what its reading represents and how it is calibrated; an altimeter is not a substitute for maps, approved flight instruments, or safety procedures.

What You’ll Need

An altimeter, such as a barometric dial or digital device
The device’s manual or legend, especially if its display has multiple fields
For an aviation altimeter: the appropriate current pressure setting from an authorized aviation source, and training in its use
For a hiking altimeter: a known elevation or reliable local pressure reference if you need to calibrate it

Step-by-Step

Identify the instrument. Check whether you have a barometric altimeter, a GPS-based display, or both. A barometric altimeter estimates altitude from air pressure. A GPS device calculates elevation from satellite positioning, which can be less reliable vertically in some conditions. A device may show either reading, so check its label or manual.
Find the units and scale. Look for “ft” for feet or “m” for meters. On an analog aviation instrument, altitude is shown on a circular dial, typically with a long hand for hundreds of feet, a shorter hand for thousands, and sometimes a small pointer for tens of thousands. Confirm the instrument’s markings before interpreting it; designs differ. On a digital device, read the number alongside its unit rather than assuming the unit from a previous screen.
Read an analog dial by place value. On a common three-pointer aircraft altimeter, combine the hands. For example, if the long hand points to 5, the thousands hand to 2, and the ten-thousands hand to 0, the indication is about 2,500 feet. Read the small hand carefully: it may be easy to confuse 2,500 with 7,500 if you read only one pointer. Use the dial labels and instrument manual to verify the interpretation.
Read a digital display directly. Find the altitude field and note the complete number and unit. Check whether it is labeled barometric altitude, GPS altitude, elevation, or something else. Do not read a nearby heading, vertical-speed value, or pressure setting as the altitude. If the display has a trend arrow, that indicates direction of change, not the current altitude itself.
Understand the reference. A pressure altimeter does not measure height from the ground directly. It senses air pressure and converts that pressure to an altitude using a standard relationship. Aviation altimeters can be set to show altitude relative to mean sea level when given the correct local pressure setting. A hiking altimeter may instead be calibrated to a known location’s elevation. A reading therefore depends on both pressure and the setting used.
Set the reference when appropriate. In aviation, use the pressure setting and procedures specified by your training and the applicable aviation authority. The setting is commonly entered through a knob that moves the small pressure window, called the altimeter setting window or Kollsman window. Confirm the setting and resulting indication using the aircraft checklist and instructor guidance. Never guess a setting or rely on an old one. For a hiking device, calibrate at a location with a known elevation, following the manual.
Check conditions and movement. Barometric readings can change as weather systems pass, and pressure also changes with altitude. If you move to a new location or the weather shifts, the indicated altitude may drift unless the device is recalibrated or updated. Allow for the instrument’s response time and avoid treating a momentary fluctuation as a precise change in elevation.
Compare with other information. When practical, compare the altimeter with a known map elevation, a marked trail point, a nearby airport report, or another suitable reference. Large disagreement may signal an incorrect setting, wrong units, poor GPS reception, or a device problem. For flight, follow approved procedures and use required instruments; casual cross-checking is not a replacement for training or air traffic instructions.

Common Mistakes

Confusing altitude with height. Altitude usually means elevation above mean sea level. Height often means distance above the local ground or another reference point. A barometric altimeter does not automatically tell you clearance above terrain.
Ignoring units. A value in meters can look plausible when you expect feet, but the difference is substantial. Verify the unit every time the display or device changes.
Reading only one dial hand. Analog pointers represent different place values. Read all of them together and use the marked scale; do not infer a full altitude from the long hand alone.
Using an outdated pressure setting. A stale or incorrect setting can make a pressure altimeter indicate an inaccurate altitude. In aviation, obtain and set the required current value as directed by official procedures.
Assuming GPS and barometric altitude must match. They use different methods and may disagree. Neither should be treated as infallible in every situation.
Treating the reading as exact. Pressure changes, calibration, device limits, and the reference point all affect accuracy. Use suitable safety margins and other navigation information.

Tips

Learn the exact display or pointer layout from the manufacturer’s manual before relying on it.
Make a habit of saying the altitude and unit together, such as “2,500 feet,” to reduce mix-ups.
For hiking, record a known elevation when calibrating and recalibrate after major weather changes or when readings no longer agree with reliable references.
For aircraft, use the approved checklist, current authorized settings, and formal training. Altimeter interpretation is only one part of safe instrument use.
Keep a device’s pressure port clear and protect it from damage; follow the manual for care and calibration rather than probing openings or making adjustments by guesswork.

Troubleshooting

The reading seems far too high or low: Check feet versus meters, confirm the displayed field, and verify the pressure or calibration setting. Compare with a known elevation or trusted reference. If it remains implausible, do not rely on it for navigation.

The reading changes while you are stationary: Weather-related pressure changes can affect a barometric altimeter. Recalibrate a recreational device to a known elevation if its manual allows. In an aircraft, follow established procedures for obtaining and setting pressure information; do not adjust based on guesswork.

A GPS altimeter is blank or unstable: Move to a location with a clearer view of the sky, check the device’s positioning status, and consult its manual. If position information is unavailable or unreliable, use another appropriate navigation method.

An analog pointer is hard to interpret: Check the dial labels and manual, then read each pointer’s place value. If the instrument is damaged, sticking, or inconsistent, have it inspected by a qualified service provider; do not use it where accuracy is safety-critical.

Frequently Asked Questions

Does an altimeter show height above the ground?

Usually, no. A standard pressure altimeter indicates altitude relative to a pressure reference, commonly mean sea level when correctly set. It does not automatically account for the ground directly beneath you.

Why does an altimeter need a pressure setting?

Air pressure changes with weather as well as altitude. A pressure setting helps the instrument translate local pressure into a more useful altitude indication. The required setting and procedure depend on the use and location.

Are feet and meters interchangeable on an altimeter?

No. They are different units, so always read the unit label alongside the number. If you need to convert, one meter is about 3.28 feet, but use the device’s stated units for operational readings.

Can I use a phone’s altimeter for aircraft navigation?

Do not use a phone or consumer device as a replacement for required aircraft instruments, training, or official aviation procedures. Use only equipment and methods approved for the operation.

Why does my altimeter disagree with a map elevation?

The map point may not be your exact location, or the device may need calibration. Weather, GPS limitations, and differences between altitude references can also cause disagreement. Check the device manual and compare with a suitable known reference.

Further reading: Federal Aviation Administration. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.