The chart below shows the amount of helium needed and average flying time for Qualatex latex balloons:

11 inch round balloon (standard colors)   -   .5 cu ft     -  18-24 hours 
11 inch round balloon (metallic or pearl)  -   .5 cu ft     -  16-18 hours
11 inch heart balloon                                -   .3 cu ft     -   8 hours
16 inch round balloon                               - 1.5 cu ft     -   30+ hours
17 inch heart shaped balloon                    -   .9 cu ft     -   14 hours
3 foot round balloon                                 - 15 cu ft      -   3 - 5 days
3 foot heart shapped balloon                    -   7 cu ft      -   3 - 5 days

18"  Foil (mylar balloon)                             -  .5 cu ft      -  1 - 2 weeks
36"  Foil (mylar balloon)                             - 4.4 cu ft     -  2 - 3 weeks

Note:  Actual flying times vary depending on temperature and atmospheric conditions.  Times listed are conservative averages.

*Using ULTRA HI-FLOAT balloon flight extender for all helium-filled latex balloons can increase the flying times of latex balloons up to 25 times longer than untreated balloons  (hi-float should not be used in foil/mylar balloons).