Speed unit conversion Convert what quantity? From:centimeter/secondfoot/secondinch/secondkilometer/hourkilometer/secondknotmachmeter/secondmile/hour (mph)mile/secondmillimeter/secondspeed of light [vacuum]speed of sound [air] To:centimeter/secondfoot/secondinch/secondkilometer/hourkilometer/secondknotmachmeter/secondmile/hour (mph)mile/secondmillimeter/secondspeed of light [vacuum]speed of sound [air] Result: speed unit conversion, speed to miles per hour,km/sec to mph.