Location technology
How GPS Works: A Plain-Language Explanation
GPS works by timing radio signals from satellites. Learn how a receiver uses them to work out position, with no internet required.
Updated 14 October 2026 · 3 min read
GPS, the Global Positioning System, works by letting a receiver measure how long radio signals take to arrive from several satellites. Each signal carries the satellite's position and the exact time it was sent. Because radio waves travel at a known speed, the delay reveals the distance to each satellite, and a few such distances are enough to compute where you are.
The satellites
GPS is operated by the United States and consists of a constellation of satellites orbiting at around 20,000 km above the Earth. They are arranged so that, from most places in open sky, several are above the horizon at any time. Each carries very precise atomic clocks and continuously broadcasts a message with its orbit and the time.
Measuring distance with time
Your receiver does not need an expensive clock. It compares the time stamp in each signal with its own clock to work out how long the signal took to travel. Multiplying that delay by the speed of light gives a distance. A distance from one satellite places you somewhere on a sphere around it. With a second satellite your position narrows to a circle where two spheres intersect, and with a third it narrows to two points, one of which is usually out in space.
Why four satellites
Receiver clocks are not perfect, and a tiny timing error becomes a large distance error because light travels so fast. A fourth satellite lets the receiver solve for its own clock offset as an extra unknown. That is why a standard fix needs signals from at least four satellites: three for position and one to correct time. More satellites in view generally improve the result.
From distance to coordinates
Once the receiver has its position in three dimensions, it converts it into latitude, longitude and height using a reference model of the Earth. For GPS, that model is WGS 84. The output you see, such as 51.5007, -0.1246, is that position written as latitude and longitude.
What GPS does not do
- It does not require a phone signal or internet.
- It does not send your location out; the satellites only transmit.
- It does not work perfectly everywhere. Buildings, trees and walls weaken or reflect signals, as covered in why phone GPS is sometimes inaccurate.
GPS and other systems
GPS is one of several satellite navigation systems. Modern phones usually listen to more than one, which improves speed and reliability. This wider family is called GNSS, and it is described in what GNSS is.
Frequently asked questions
Does GPS need an internet connection?
No. A GPS receiver calculates its position from satellite signals alone. Phones often use data to speed up the first fix, but it is not required for the position itself.
Does GPS track my phone?
GPS is receive-only. The satellites broadcast and your device listens, so GPS itself does not send your position anywhere. Apps and services are what share it.