Science, Tech, Math › Science What Is The Speed Of Light In Miles Per Hour? Unit Conversion Example Problem Share Flipboard Email Print Nick Koudis, Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Todd Helmenstine Todd Helmenstine is a science writer and illustrator who has taught physics and math at the college level. He holds bachelor's degrees in both physics and mathematics. our editorial process Todd Helmenstine Updated January 04, 2019 This unit conversion example problem demonstrates how to convert the speed of light in meters per second to miles per hour. Problem The speed of light in a vacuum is 2.998 x 108 m/sec. What is this speed in miles per hour? Solution To convert this measurement, we need to convert meters to miles and seconds to hours. To do this, we need the following relationships:1000 meter = 1 kilometer1 kilometers = 0.621 mile60 seconds = 1 minute60 minutes = 1 hourWe can now set up the equation using these relationships so the units cancel out leaving only the desired miles/hour.speedMPH = 2.998 x 108 m/sec x (1 km/1000 m) x (0.621 mi/1 km) x (60 sec/1 min) x (60 min/1 hr)Note all the units cancelled out, leaving only miles/hr:speedMPH = (2.998 x 108 x 1/1000 x 0.621 x 60 x 60) miles/hrspeedMPH = 6.702 x 108 miles/hr Answer The speed of light in miles per hour is 6.702 x 108 miles/hr.