# How to predict the weight of helium?

I have a balloon, which weighs 10 grams. now i fill it with helium (x gram)... since I added helium into the balloon. now the weight should be 10+x grams... but the balloon goes upwards. Shape of the balloon is irregular so I cannot find the volume. How to measure the weight of the helium?

Then weigh the sand. Say this weight is $W_s$, the weight of the balloon shell is $W_b$, volume is $V$, weight of helium in the balloon is $W_h$, and density of air is $\rho_a$. Then the following will hold true:
$W_s + W_b + W_h = \rho_a V$