Fuel flow rate gauge

does anyone know of any sensor that can measures fuel consumption rate like in per second or perkm or something then display it on a gaude meter. they must have invented that already cause that can help a lot to budget fuel. It seems like i cant find it and its been frustrating for me.

i've tried obd-II. the sensor read values that are meant to troubleshoot for problems. there is no way to determine the fuel flow rate. it got everything else you need but no fuel flow rate. fuel flow rate................

the display should be in real time of course