April Fools: A Fermi Problem

After hearing several hours of lecture from Dr. C.Y. Chien on Fermi estimation problems, the physics grad students felt we owed him one. We invited Dr. Chien and the physics department at large to make their own estimate: how many balloons does it take to fill the foyer in the main office?


  • Total balloons inflated, filling foyer & mailroom: 2500
  • Balloons filling foyer only: **1670 +/- 20 ** (some popped)
  • Our initial estimate for foyer only: 1400 (based filling a 3-meter cube with 30-cm balloons at 72% packing efficiency)
  • Time to fill foyer: 3 1/2 hours with 6-8 people working at any given time