Edit in JSFiddle


              
Xăng còn 4.5 lít:
<meter min="0" max="5" low="1" high="4" optimum="5" value="4.5"></meter><br>
Xăng còn 2.5 lít:
<meter min="0" max="5" low="1" high="4" optimum="5" value="2.5"></meter><br>
Xăng còn 0.5 lít: 
<meter min="0" max="5" low="1" high="4" optimum="5" value="0.5"></meter><br>