Helium Required to Lift Given Payload?

I am launching a weather balloon to 35km altitude. I am currently writing a python script which tells me the volume a given amount of helium will occupy at a given pressure and temperature. Being a year eight student i am having some problems understanding the ideal gas law. Is this correct?

n = # of moles
r = 8.31447
t = Temperature (c)
p = Pressure <KPA>

v = (n*r*t)/p

If so, does this work?
Convert grams to moles: 163g of helium * 0.249837480719
n = 163*0.249837480719
n = 40.7235094
r = 8.31447
t = 25(c)
p = 95.91 kPa
v = (n*r*t)/p
v = (40.7235094*8.31447*25)/95.91
v = 88.2583665 Liters

Is this correct?