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Neither is always more accurate. For local elevation readings on a recreational device, a properly calibrated barometric altimeter can be more accurate when air pressure is stable. GPS altitude can be useful when the device has a good view of the sky, but its accuracy varies with satellite geometry, obstructions, atmospheric conditions and receiver design. The right choice depends on whether you need elevation at one point, a record of elevation change, or an aviation instrument reading.
What each altimeter measures
GPS altitude
A GPS receiver estimates its position using signals from satellites. Its altitude is part of that position estimate, so it is affected by the satellite geometry available to the receiver, signal quality and the receiver itself. Buildings, bridges and trees can obstruct signals; reflected signals can also contribute to positioning errors. A display in feet or metres does not make a GPS altitude equivalent to an elevation measured by another method.
GPS.gov distinguishes the performance of the GPS service from the accuracy a user gets. Its accuracy guidance says user accuracy depends on satellite geometry, user range error, local signal blockage, atmospheric conditions and receiver design and quality. A clear sky view generally gives the receiver a better opportunity to obtain a useful position, but it does not turn a system-level statistic into a guarantee for an individual reading.
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GPS altitude is therefore an estimate produced at a particular time and place. Moving a receiver from an open ridge to a canyon, under a bridge or beside a tall building can change the signal environment even when the actual elevation has not changed. A single fix may also differ from the next fix because the available satellites and their geometry have changed. These effects are why a strong horizontal position indication does not automatically mean the vertical result is equally strong.
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Barometric altitude
A barometric altimeter estimates elevation from ambient air pressure. Pressure changes as elevation changes, so a pressure sensor can register a climb or descent. But the same sensor can also register pressure changes caused by weather. The device therefore needs a reference: calibration to a known elevation or, on some models, another pressure-based input.
Calibration matters because the instrument is interpreting pressure as elevation. A device calibrated at a known point starts from a more useful local reference than one calibrated using a less accurate estimate. If ambient pressure changes after calibration, the displayed elevation can drift even if the device has not moved. This is why manufacturer accuracy statements for recreational barometric altimeters are conditional on pressure remaining stable.
A barometer is especially useful for relative movement. A steady pressure sensor can show that you climbed or descended even when its absolute elevation has a small offset. It cannot, however, distinguish every weather-related pressure change from a change in height. On a day with a falling or rising pressure system, a stationary device may slowly report a descent or climb.
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“Accuracy” can mean several different things in this comparison. Absolute elevation is how closely the displayed value matches a trusted elevation for the same point. Elevation change is how well the device records a climb or descent between two points. Repeatability is whether repeated readings under the same conditions stay close to one another. A device can be useful for tracking a route while still having an absolute offset, and a reading can be close to a known elevation once but drift later as pressure changes.
For a hiking decision, ask which of these you actually need. If you want to know whether a pass is roughly 2,000 feet higher than the trailhead, consistent change may matter most. If you need to confirm your position at a marked elevation, absolute agreement with that reference matters more. Neither recreational GPS nor a recreational barometric altimeter should be treated as a survey instrument.
What the published accuracy figures do—and do not—show
The available figures come from different sources, describe different conditions and are not the result of a controlled head-to-head test. In particular, GPS.gov’s vertical service-performance statistics should not be directly compared with Garmin’s conditional specifications for selected outdoor devices as if both were measured on the same device, route or day.
| Measure | Published figure | Scope and qualification |
|---|---|---|
| Typical smartphone GPS positioning | Within a 4.9 m (16 ft.) radius under open sky | GPS.gov’s consumer example, accessed in 2026. It describes positioning accuracy, not an altitude-accuracy promise. |
| GPS Standard Positioning Service vertical error | Global average: ≤13 m (about 43 ft.) at 95% probability | GPS.gov’s performance page reports a 2023 performance analysis. This is a service performance measure, not a guarantee for an individual receiver. |
| GPS Standard Positioning Service vertical error at the worst site | ≤33 m (about 108 ft.) at 95% probability | GPS.gov’s reported 2023 performance analysis. This is also a service measure, not an individual-device guarantee. |
| Selected Garmin GPSMAP 64/65 barometric altimeters | Within ±50 ft. when properly calibrated | Garmin Customer Support’s guidance, accessed in 2026, applies while weather conditions are stable and ambient pressure is not changing. |
| GPS calibration on the cited Garmin handhelds | Within ±400 ft. | Garmin Customer Support’s stated accuracy for calibrating the cited handheld by GPS; it is not the same calibration result as using a known elevation. |
| Selected Garmin outdoor devices at a given point | Within ±10 ft. | Garmin Support’s guidance, accessed in 2026, applies to properly calibrated devices when ambient pressure is not changing. |
The figures point toward a practical conclusion, not a universal ranking: under the stated stable-pressure conditions, the cited barometric specifications can support more precise local elevation readings than the general GPS vertical service figures. That comparison is still limited by the devices and conditions described above. It does not establish that every barometric altimeter beats every GPS receiver, or that either figure will describe your reading in the field.
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Do not substitute the 4.9 m smartphone example for an altitude specification. It is a horizontal positioning example. Likewise, do not read the GPS vertical performance figures as a prediction that every consumer GPS altitude will be within that distance. The service statistics and a particular receiver’s performance answer different questions.
Which one should you use?
For local elevation at a known point
Use a barometric altimeter calibrated to a trusted known elevation if the device and conditions fit the manufacturer’s stated accuracy. That gives the pressure measurement a local reference. If the device offers GPS calibration as an alternative, do not assume it provides the same result as calibration against a known elevation: Garmin publishes different accuracy figures for those inputs on its cited handhelds.
Examples of useful references include a clearly identified trailhead, a surveyed benchmark or another elevation you trust. The reference must describe the same point where you are standing; calibrating at a nearby but different elevation can simply transfer that difference into the device. Record the reference and the time of calibration so you know what baseline the reading uses.
For tracking a hike’s climbs and descents
A barometric altimeter is a useful choice for following elevation change when it is calibrated and pressure is not shifting significantly. Weather-related pressure changes can look like elevation changes to the sensor, so a long outing or changing conditions can make the reading drift. Check against a known elevation when practical, and interpret the trace as an instrument reading rather than a surveyed elevation profile.
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For a point where you do not know the elevation
GPS can supply an estimate without a local elevation reference, but its reliability depends on the signal environment and receiver. A barometric reading also needs a useful calibration reference; an uncalibrated pressure reading should not be treated as a dependable absolute elevation. If accuracy matters, compare the device with a trusted known elevation and recalibrate as its instructions allow.
For a canyon, forest or city
These are difficult environments for GPS because buildings, bridges and trees can block or reflect signals. A barometric device may continue to provide a smooth relative trace, but only if its pressure reference remains valid. In a canyon or wooded route, check the barometric reading at a known point before relying on it for an absolute value, and avoid treating a momentary GPS fix as definitive.
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For surveying, weather prediction or other precise work
Do not rely on recreational outdoor devices for precise measurement. Garmin explicitly cautions that its outdoor devices should not be used for activities requiring precise measurements, including surveying or weather prediction. Use equipment and procedures appropriate to the task.
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Calibrate a barometric altimeter
- Find a trustworthy reference. When you are at a location with a known elevation, use that as the calibration input if your device supports it. A known elevation is preferable to GPS calibration in the cited Garmin guidance.
- Check the conditions. Note whether weather is changing. The published ±50-foot and ±10-foot figures are conditional on stable ambient pressure; calibration cannot prevent later drift caused by a pressure change.
- Follow the instructions for your exact model. The calibration menus and available inputs vary by device. Garmin’s guidance for GPSMAP 64/65 describes calibration by known elevation or GPS altitude; its 66/67 support information also lists known elevation and sea-level pressure as inputs. Use the model-specific instructions rather than assuming a menu path or procedure is shared across models.
- Enter the reference carefully. A wrong elevation, wrong unit or wrong location creates a systematic error that may look like sensor failure. Confirm whether the device asks for elevation, pressure or a sea-level pressure value before saving the calibration.
- Recheck the reading at another known point when practical. This helps reveal calibration error or drift. If weather has changed, a difference may reflect changing ambient pressure rather than a change in the physical elevation.
- Recalibrate when your reference changes. Moving to a new area, encountering a substantial weather change or restarting after a long interval can make an earlier pressure reference less representative. Use the model’s instructions and a trusted reference whenever possible.
Improve a GPS altitude estimate
- Give the receiver the clearest available view of the sky; buildings, bridges and trees can degrade positioning.
- Be cautious around reflective or obstructed environments, where signals may be blocked or reflected.
- Allow the receiver to obtain a position before recording an important reading, rather than relying on the first displayed value.
- Do not infer altitude accuracy from a device’s horizontal-position specification or a general GPS service statistic.
- When the elevation matters, check against a trusted known elevation instead of treating one GPS fix as definitive.
- If the device reports both sensor types, note which source is selected. Switching between GPS and barometric modes can create an apparent jump that is really a change in measurement method.
Why altitude readings can disagree
Disagreement is not automatically evidence that one instrument has failed. The two readings can be responding to different sources of error. GPS altitude is affected by the satellite and signal conditions at the receiver. Barometric altitude is affected by calibration and by pressure changes unrelated to movement. Their displayed units may be identical while their underlying estimates are not.
- The barometer changes while you remain still: ambient pressure may have changed, so the device’s pressure-based elevation estimate may drift.
- The GPS reading varies between locations or moments: the receiver may have a different satellite geometry or signal environment, or be affected by obstruction or reflected signals.
- The two readings differ by a constant amount: one device may have an offset from its calibration reference. Compare both with a known elevation before deciding which is preferable.
- The difference grows during a storm or pressure trend: changing weather is a likely explanation for barometric drift, although it does not prove that GPS is correct.
- Both readings differ from a map or sign: check the reference’s reliability, the device’s calibration, and whether the readings represent the same point and conditions before concluding that either method is inaccurate.
For a recreational device, the sensible response is to establish a reference and examine the conditions—not to average the two numbers automatically. The cited sources do not establish a standardized method for combining the readings or a universal threshold at which one should override the other.
A simple decision guide
| Your priority | Usually the better starting point | What to verify |
|---|---|---|
| Absolute elevation at a marked location | Calibrated barometric altimeter | Known elevation reference and stable pressure |
| Elevation gain on a hike | Barometric altimeter, with a GPS cross-check | Calibration before the outing and weather changes during it |
| Estimate where no reference is available | GPS altitude | Open sky, good signal environment and receiver quality |
| Dense forest, urban streets or canyons | Whichever source can be checked against a known point; often use both | GPS blockage/reflections and barometric drift |
| Surveying, regulated aviation or other precision work | Purpose-built, approved equipment | Applicable professional procedures, not recreational specifications |
Aviation altimeters are a separate case
Aircraft use barometric altimeters within regulated procedures and maintenance contexts. Recreational GPS and outdoor-device specifications are not a substitute for aviation instruments, settings or procedures. The FAA Aeronautical Information Manual says that when an aircraft altimeter’s indicated altitude differs from known field elevation by plus or minus 75 feet or more, its accuracy is questionable and the matter should be referred to a rated repair station for evaluation. That is aviation guidance, not a consumer-device comparison or a general recreational tolerance.
The FAA threshold should not be copied into a hiking watch or handheld GPS. Aircraft altimeter settings, field-elevation checks and repair-station evaluations belong to a regulated system with different instruments and responsibilities. A consumer device showing a 75-foot difference does not automatically meet or fail an aviation requirement.
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Some recreational handheld GPS devices include both satellite navigation and a barometric altimeter. That combination can offer separate position and pressure-based elevation readings, but having both sensors does not remove the need to understand calibration, pressure changes and signal conditions. Garmin documents calibration and feature behavior for GPSMAP 64/65 and 66/67 series devices; the figures in this article apply only to the cited manufacturer guidance and its stated conditions.
When comparing devices, look for a clearly documented barometric sensor, the calibration inputs it accepts, and the conditions attached to any accuracy claim. Confirm whether the device lets you calibrate to a known elevation, GPS altitude or sea-level pressure. Also check whether the display identifies the active altitude source, because a device that can switch sources may show different values without either sensor being defective.
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Battery life, mapping and satellite reception can affect how conveniently you collect readings, but no feature list replaces a reliable reference. A product with both sensors gives you a way to compare independent estimates; it does not guarantee that they will agree or that either one is suitable for precision work.
There is no basis here to name a current model as the most accurate or to claim a tested winner. When choosing a navigation device, check whether it has a barometric altimeter, what calibration inputs it supports, and the manufacturer’s conditions for any stated accuracy. Then match those capabilities to the task: elevation tracking on a hike is not the same requirement as an absolute elevation measurement or an aviation reading.
Bottom line
For a properly calibrated recreational device in stable weather, a barometric altimeter is often the stronger choice for local elevation and elevation-change tracking. GPS altitude is valuable when you lack a local reference and have a clear sky view, but its vertical accuracy depends on satellite geometry, blockage, atmospheric conditions and receiver design. Published figures are conditional and come from different measurement contexts, so they do not produce a universal winner. Calibrate to a trusted elevation when possible, check the surroundings and weather, and use professional equipment whenever the measurement must be precise.
Frequently Asked Questions
Is GPS or a barometric altimeter more accurate for hiking?
For a properly calibrated recreational device and stable weather, a barometric altimeter can provide more accurate local elevation and a smoother elevation-change track. GPS may be preferable when you have no known elevation reference or when the barometer has not been calibrated. In forests, canyons and cities, GPS obstructions can reduce its reliability; changing pressure can make the barometer drift.
What does GPS.gov’s 4.9 m accuracy figure mean?
It is a typical open-sky horizontal positioning example for GPS-enabled smartphones. It is not a promise that the phone’s altitude will be within 4.9 metres.
How accurate is consumer GPS altitude?
GPS.gov reports a global average vertical error target of no more than 13 metres, about 43 feet, at 95% probability, and a worst-site target of no more than 33 metres, about 108 feet, at 95% probability, for GPS Standard Positioning Service performance. These are system statistics, not guarantees for an individual consumer receiver.
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How accurate is a barometric altimeter?
Accuracy depends on the device, calibration and pressure stability. Garmin states that selected properly calibrated GPSMAP 64/65 barometric altimeters can report elevations within ±50 feet while ambient pressure is not changing. A separate Garmin support page gives ±10 feet at a given point for specified properly calibrated outdoor devices under the same stable-pressure condition.
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Is calibrating by GPS good enough?
It can provide a usable reference, but it is not equivalent to calibration at a known elevation. Garmin states ±400 feet for GPS calibration on the cited handhelds and ±50 feet when properly calibrated under stable conditions, with the exact context and model limitations applying. Use a trusted known elevation when available.
Why does my barometric altitude change while I am standing still?
Ambient pressure can change because of weather. The sensor interprets that pressure change as an elevation change, so the displayed altitude may drift even though you have not moved. Recheck against a known elevation and recalibrate according to the device instructions when practical.
Why do GPS and barometric altitude disagree?
They measure different things and have different error sources. GPS is affected by satellite geometry, signal blockage, reflected signals, atmospheric conditions and receiver design. Barometric altitude is affected by its calibration and by pressure changes. A difference alone does not identify which reading is correct.
Can I use a recreational altimeter for surveying or weather prediction?
No. Garmin cautions that its outdoor devices are recreational navigation aids and should not be used for precise measurements such as surveying or weather prediction. Use equipment and procedures designed for the specific professional task.
Does the FAA’s 75-foot figure apply to hiking GPS devices?
No. The FAA Aeronautical Information Manual uses a plus-or-minus 75-foot difference from known field elevation as a reason to question an aircraft altimeter and refer it to a rated repair station. That is aviation maintenance guidance, not a tolerance for consumer outdoor devices.
The Bottom Line
Choose the sensor for the job. A calibrated barometric altimeter is usually the better recreational tool for local elevation and climb tracking when pressure is stable. GPS is useful without a local reference and in open sky, but its vertical reading can be degraded by geometry, blockage, reflections and receiver quality. Neither recreational method replaces professional equipment for precision work.
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