GPS Accuracy

The U.S. government is committed to providing GPS to the civilian community at the performance levels specified in the GPS Standard Positioning Service (SPS) Performance Standard. For example, the GPS signal in space will provide a "worst case" pseudorange accuracy of 7.8 meters at a 95% confidence level. (This is not the same as user accuracy; pseudorange is the distance from a GPS satellite to a receiver.) View document

Histogram of global GPS horizontal position error from 1 January to 31 March 2014, with a peak just around 1 m and a line showing 95% of the readings were at or below 3.286 m
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FAA data collected in early 2014 shows the horizontal accuracy of GPS SPS is often within ~1 m
Bar chart of SPS signal-in-space user range error (URE) in 2001 (1.6 meter), 2002 (1.4 meter), 2003 (1.2 meter), 2004 (1.2 meter), 2005 (1.1 meter), 2006 (1.1 meter), 2007 (1.0 meter), 2008 (1.0 meter), 2009 (0.9 meter), 2010 (0.9 meter), 2011 (0.9 meter), 2012 (0.8 meter), and 2013 (0.8 meter), with notations that the 2001 SPS performance standard required 6 meter URE and the 2008 standard was 4 meters. Signal-in-space URE is the difference between a GPS satellite's navigation data (position and clock) and the truth, projected on the line-of-sight to the user.
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Air Force data shows increasing GPS signal-in-space accuracy from 2001 to 2013

The actual accuracy users attain depends on factors outside the government's control, including atmospheric effects, sky blockage, and receiver quality. Real-world data from the FAA show that their high-quality GPS SPS receivers provide better than 3.5 meter horizontal accuracy.

Higher accuracy is attainable by using GPS in combination with augmentation systems. These enable real-time positioning to within a few centimeters, and post-mission measurements at the millimeter level. Learn more

The U.S. government is committed to modernizing the GPS constellation to enable higher civilian accuracy without augmentations. The first of many next-generation GPS satellites launched in 2005. Learn more

Is Military GPS More Accurate Than Civilian GPS?

The accuracy of the GPS signal in space is actually the same for both the civilian GPS service (SPS) and the military GPS service (PPS). However, SPS broadcasts on one frequency, while PPS uses two. This means military users can perform ionospheric correction, a technique that reduces radio degradation caused by the Earth's atmosphere. With less degradation, PPS provides better accuracy than the basic SPS.

Many users enhance the basic SPS with local or regional augmentations. Such systems boost civilian GPS accuracy beyond that of PPS. Learn more

The ongoing GPS modernization program is adding new civilian signals and frequencies to the GPS satellites, enabling ionospheric correction for all users. Eventually, the accuracy difference between military and civilian GPS will disappear. But military GPS will continue to provide important advantages in terms of enhanced security and jam resistance. Learn more

What About Selective Availability (SA)?

During the 1990s, GPS employed a feature called Selective Availability that 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 SA again.

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