Recommended Free Tools
GPS works by having satellites broadcast precise timing and orbit information that a receiver—such as a phone—uses to calculate its own position. The satellites do not need to receive a signal from your phone: a GPS receiver listens to several satellites, estimates how long their signals took to arrive, and uses those measurements to work out location and time.
What GPS is—and what it is not
The Global Positioning System is a U.S.-owned utility that provides positioning, navigation, and timing (PNT) services. It is operated by the U.S. Space Force. GPS is one satellite navigation system; a phone may also use signals from other satellite systems, but that does not change how GPS itself works.
GPS has three parts: satellites in space that broadcast signals, a ground control segment that monitors and maintains the system, and user equipment that receives the signals and calculates its position and time. The receiver—not the satellite—does the location calculation. GPS.gov’s overview of the system describes these segments and their roles.
How a GPS receiver calculates a position
1. Satellites broadcast time and navigation data
Each GPS satellite transmits a radio signal containing information about when the signal was sent and where the satellite was in orbit at that time. The broadcast is one-way: ordinary GPS receivers listen, rather than sending a location request back to the satellites.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →#1 Best Overall
- Bright, high-resolution 5” glass capacitive touchscreen display lets you easily view your route
- Get more situational awareness with alerts for school zones, speed changes, sharp curves and more
- View food, fuel and rest areas along your active route, and see upcoming cities and milestones
- View Tripadvisor traveler ratings for top-rated restaurants, hotels and attractions to help you make the most of road trips
- Directory of U.S. national parks simplifies navigation to entrances, visitor centers and landmarks within the parks
2. The receiver estimates distance from signal travel time
Radio signals travel at the speed of light. By comparing the signal’s send time with its arrival time, the receiver estimates how far the signal traveled. The result is called a pseudorange, not a perfect distance: small errors in the receiver’s clock and in how the signal travels through the atmosphere can affect it.
3. Measurements from multiple satellites narrow down the location
Imagine each measured range as a sphere centered on a satellite. The receiver must be somewhere on that sphere. Ranges from additional satellites create further spheres; where they intersect, they constrain the receiver’s location. This method is commonly called trilateration—it uses distances, not angles.
Rank #2
- 6” high-resolution navigator includes map updates of North America
- Hands-free calling when paired with your compatible smartphone with BLUETOOTH technology and convenient Garmin voice assist lets you ask for directions to places you want to go
- Road trip–ready features include the HISTORY database of notable sites, a U.S. national parks directory, Tripadvisor traveler ratings and millions of Foursquare POIs
- Driver alerts for things such as school zones, sharp curves and speed changes help encourage safer driving and increase situational awareness
- Access live traffic, fuel prices, parking, weather and smart notifications when you pair this navigator with your compatible smartphone running the Garmin Drive app
In ordinary three-dimensional positioning, the receiver needs signals from at least four satellites to solve for three position coordinates and its own clock offset. That fourth measurement helps account for the fact that a phone’s clock is not as precisely synchronized as the atomic clocks aboard GPS satellites. With more usable signals, a receiver can have additional measurements to work with.
What the ground control segment does
Ground stations monitor satellite health and signals, track and maintain satellite orbits, adjust satellite clocks, and upload updated navigation data. This keeps the broadcast information usable and the constellation operating as intended. Control stations maintain the system; they do not calculate each phone’s position.
Rank #3
- Explore confidently with the reliable handheld GPS
- 2.2” sunlight-readable color display with 240 x 320 display pixels for improved readability
- Preloaded with Topo Active maps with routable roads and trails for cycling and hiking
- Support for GPS and GLONASS satellite systems allows for tracking in more challenging environments than GPS alone
- 8 GB of internal memory for map downloads plus a micro SD card slot
How many GPS satellites are there?
The nominal GPS constellation is 24 satellites arranged in six equally spaced orbital planes, with four baseline slots in each plane. GPS satellites orbit at approximately 20,200 km (12,550 miles) above Earth in medium Earth orbit and circle the planet twice per day. The U.S. commitment is to maintain at least 24 operational satellites 95% of the time; more than 24 are normally in service so coverage can continue when satellites are serviced or retired. See GPS.gov’s space-segment description.
Does GPS work without internet or cellular service?
Yes. A GPS receiver can receive satellite signals and calculate a position without an internet connection or cellular service. The satellite-to-receiver GPS signal is one-way, so the satellite does not need a phone’s data connection to find it.
Rank #4
- 8” navigator with high-resolution, dual-orientation display and map updates of North America .Special Feature:Large Display; Voice Assist; Hands-Free Calling; Live Traffic and Weather; Traffic Cams and Parking; Smart Notifications,Driver Alerts; Tripadvisor; National Parks Directory; Find Places by Name; Garmin Real Directions Feature.
- Hands-free calling when paired with your compatible smartphone with BLUETOOTH technology and convenient Garmin voice assist lets you ask for directions to places you want to go
- Road trip–ready features include the HISTORY database of notable sites, a U.S. national parks directory, Tripadvisor traveler ratings and millions of Foursquare POIs
- Driver alerts for things such as school zones, sharp curves and speed changes help encourage safer driving and increase situational awareness
- Access live traffic, fuel prices, weather, parking and smart notifications when you pair this navigator with your compatible smartphone running the Garmin Drive app
However, a phone may use cellular, Wi-Fi, or internet assistance to acquire a position more quickly or to provide other features, such as downloading maps or traffic information. Those services can be unavailable even when the phone can still calculate a GPS position; a map app may also need maps saved offline to show useful detail without a connection.
How accurate is GPS?
There is no single accuracy figure that applies to every device and environment. GPS.gov says the U.S. government commits to a daily global average user range error (URE) of no more than 2.0 m (6.6 ft.), with 95% probability across healthy satellites in constellation slots. This describes signal-in-space range performance—not the position error a person will see on an individual device.
Best Value
- Bright, high-resolution 5” glass capacitive touchscreen display lets you easily view your route
- Get more situational awareness with alerts for school zones, speed changes, sharp curves and more
- View food, fuel and rest areas along your active route, and see upcoming cities and milestones
- View Tripadvisor traveler ratings for top-rated restaurants, hotels and attractions to help you make the most of road trips
- Directory of U.S. national parks simplifies navigation to entrances, visitor centers and landmarks within the parks
GPS.gov, citing the Institute of Navigation, describes smartphone accuracy as typically within a 4.9 m (16 ft.) radius under open sky. That is a typical, condition-specific figure, not a guarantee for every phone or location. GPS.gov notes that a user’s result also depends on satellite geometry, signal blockage, atmospheric conditions, and receiver design and quality. For the official explanation, see GPS.gov’s GPS accuracy guidance.
- Open sky versus obstruction: Buildings, trees, and other obstacles can block or weaken satellite signals.
- Satellite geometry: The satellites’ positions in the sky affect how well the receiver can constrain its location.
- Atmosphere: Signal travel through the atmosphere can introduce measurement error.
- Receiver design and quality: Antenna and receiver characteristics affect how well a device can use the signals.
Which signals does GPS use?
GPS broadcasts civil signals on L1, L2, and L5 frequencies. The official interface specifications define how these signals work, including civil signal material for L2; GPS users are not required to use military signals to receive GPS. GPS.gov maintains the interface-control document and specification catalog. The specific document revisions can change, so consult that catalog for current versions.
Some specialized receivers can use multiple frequencies or correction and augmentation techniques. Those capabilities vary by equipment and application; they are not required for the basic satellite-timing method described above.
Why GPS can give both position and time
The same signal timing that lets a receiver estimate distances also provides a highly precise time reference. Once it has solved for its own clock offset, the receiver can determine time as well as position. GPS timing is used in systems beyond navigation, including infrastructure that needs synchronized clocks.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
