We derive formulas for the energy J(n) that a station's radio consumes when it transmits 1 MB of data in an IEEE 802.11 network with n stations. Calculations show that J(n) grows approximately linearly with n, for n >= 4. The useful energy consumed in successful transmission and reception of data is constant; the remaining energy is wasted. When n = 15, the waste amounts to 80 percent of total energy, and this proportion grows with n. More than 60 percent of the waste is due to overhearing-reception of packets intended for another station. Overhearing can be eliminated by using information in RTS/CTS packets.