How Does GPS Work
Last updated: March 31, 2026
Quick Answer: GPS uses 24+ satellites orbiting Earth that broadcast their position and time. Your device picks up signals from 4+ satellites, calculates distance to each based on signal travel time, and uses trilateration to pinpoint your location.
Key Facts
- GPS stands for Global Positioning System, built by US Department of Defense
- 4 satellites minimum needed for a 3D fix
- GPS satellites orbit at 20,200 km altitude
- Civilian GPS accuracy is typically 3-5 meters
- Each satellite carries atomic clocks accurate to one billionth of a second
The Basics
Three segments: space (satellites), control (ground stations), and user (your device). At any point on Earth, 4+ satellites are visible.
Step by Step
1. Each satellite broadcasts its position and precise time.
2. Your device picks up signals from 7-12 satellites.
3. It calculates distance by measuring signal travel time (radio waves travel at light speed).
4. With 3 distances = 2D position. 4th satellite adds altitude and corrects clock errors.
Why 4 Satellites?
Your phone's quartz clock isn't precise enough. The 4th signal corrects clock error — a 1 microsecond error = 300 meter position error.
Other Systems
- GLONASS: Russia (24 satellites)
- Galileo: EU (30 satellites)
- BeiDou: China (44 satellites)
Sources
- Wikipedia — GPS CC-BY-SA-4.0
- GPS.gov public_domain