How Does GPS Measure Distance?

How does your phone find where you are from GPS satellites without ever sending them a signal? It times their signals. Under open sky, a phone can usually find you to within about 16 feet (4.9 m), using satellites about 12,550 miles (20,200 km) up. Each signal travels at the speed of light, about 186,000 miles (300,000 km) every second, so if a signal took 0.07 seconds to arrive, the satellite is about 13,000 miles (21,000 km) away. This video also shows how distances become circles on a flat map and spheres in three dimensions (trilateration), why a clock error of just one millionth of a second shifts every distance by nearly 1,000 feet (about 300 m), and why GPS uses a fourth satellite to solve for your position and your phone's clock error. Try it yourself: ▶ https://www.metric-conversions.org/length/kilometers-to-miles.htm ▶ https://www.metric-conversions.org/length/meters-to-feet.htm Chapters: 0:00 The question 0:25 From time to distance 1:22 Circles on a flat map 1:48 Spheres in three dimensions 2:08 The clock problem Sources: • GPS.gov: GPS Accuracy (archive): https://archive.gps.gov/systems/gps/performance/accuracy/ • GPS.gov: Space Segment (archive): https://archive.gps.gov/systems/gps/space/ • Global Positioning System – Wikipedia: https://en.wikipedia.org/wiki/Global_Positioning_System • Pseudorange – Wikipedia: https://en.wikipedia.org/wiki/Pseudorange • NIST CODATA: speed of light: https://physics.nist.gov/cgi-bin/cuu/Value?c Is there anything else you'd like us to cover? Let us know in the comments below.