GPS Accuracy

How accurate is GPS?

It depends. GPS satellites broadcast their signals in space with a certain accuracy, but what you receive depends on additional factors, including satellite geometry, signal blockage, atmospheric conditions, and receiver design features/quality.

For example, GPS-enabled smartphones are typically accurate to within a 4.9 m (16 ft.) radius under open sky (view source at ION.org). However, their accuracy worsens near buildings, bridges, and trees.

High-end users boost GPS accuracy with dual-frequency receivers and/or augmentation systems. These can enable real-time positioning within a few centimeters, and long-term measurements at the millimeter level.

Why does GPS sometimes show me in the wrong place?

Many things can degrade GPS positioning accuracy. Common causes include:

  • Satellite signal blockage due to buildings, bridges, trees, etc.
  • Indoor or underground use
  • Signals reflected off buildings or walls ("multipath")

Cartoon of GPS signals being blocked and reflected by buildings

Far less common causes may include:

  • Radio interference or jamming
  • Major solar storms
  • Satellite maintenance/maneuvers creating temporary gaps in coverage
  • Improperly designed devices that do not comply with GPS Interface Specifications

In many cases, a device's GPS hardware is working fine, but its mapping software is faulty. For example, users are often misled by:

  • Incorrectly drawn maps
  • Mislabeled businesses and other points of interest
  • Missing roads, buildings, communities, etc.
  • Incorrectly estimated street addresses

The U.S. government cannot correct mapping errors in consumer devices. Please report them to the responsible parties using the links in our Address, Route, and Map Problems section. Go there

For help with GPS problems that are not mapping errors, please visit our GPS Service Outages & Status Reports page. Go there

What is the government's commitment to GPS accuracy?

The government is committed to providing GPS at the accuracy levels specified in the GPS Standard Positioning Service (SPS) Performance Standard. View document

The accuracy commitments do not apply to GPS devices, but rather to the signals transmitted in space. For example, the government commits to broadcasting the GPS signal in space with a global average user range error (URE) of ≤7.8 m (25.6 ft.), with 95% probability. Actual performance exceeds the specification. On May 11, 2016, the global average URE was ≤0.715 m (2.3 ft.), 95% of the time.

To be clear, URE is not user accuracy. User accuracy depends on a combination of satellite geometry, URE, and local factors such as signal blockage, atmospheric conditions, and receiver design features/quality.

User Range Error (URE) vs. User Accuracy

graphic: user receiving multiple pseudoranges, with user range error labeled on the psuedoranges and user accuracy shown as a circle around the user
To calculate its position, a GPS device measures its distance (range) from multiple GPS satellites. URE is a measure of ranging accuracy. User accuracy refers to how close the device's calculated position is from the truth, expressed as a radius.

The ongoing GPS modernization program will further improve accuracy for civilian and military users. Learn more

Is military GPS more accurate than civilian GPS?

The user range error (URE) of the GPS signals in space is actually the same for the civilian and military GPS services. However, most of today's civilian devices use only one GPS frequency, while military receivers use two.

Using two GPS frequencies improves accuracy by correcting signal distortions caused by Earth's atmosphere. Dual-frequency GPS equipment is commercially available for civilian use, but its cost and size has limited it to professional applications.

With augmentation systems, civilian users can actually receive better GPS accuracy than the military. Learn more

Doesn't the government degrade civilian GPS accuracy?

No. During the 1990s, GPS employed a feature called Selective Availability that intentionally degraded civilian accuracy on a global basis.

In May 2000, at the direction of President Bill Clinton, the U.S. government ended its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.

The United States has no intent to ever use Selective Availability again. Learn more

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