noun

an instrument that measures and gives a visual display of the amount, level, or contents of something.

a fuel gauge

measuring instrument,measuring device,meter,measure,indicator,dial,scale,index,display

verb

estimate or determine the amount, level, or volume of.

astronomers can gauge the star’s intrinsic brightness

measure,calculate,compute,work out,determine,ascertain,count,weigh,quantify,put a figure on