In this interdisciplinary lab, students integrate chemistry and physics concepts by measuring the volume of helium gas in an irregularly-shaped Mylar balloon. It provides a simple way for students to investigate Archimedes' Principle and the Ideal Gas Law. Advanced classes can perform detailed uncertainty analysis and correct the gas constant to account for moisture in the air. At either level, the lab allows learners to calculate the volume of an irregular shape with uncertainty of <2%. A key takeaway is that scientists in real labs take care to do measurement and calculation within acceptable parameters of accuracy and precision.