We have measured the complete 1.7 &mgr;m excited state absorption (ESA) spectrum in erbium‐doped glasses. The spectrum is obtained by measuring the gain of an erbium‐doped waveguide in the 1400–1800 nm region. Using the measured spectra, we estimate the 1.5 &mgr;m uniform upconversion rate by calculating the spectral overlap between the 1.5 &mgr;m emission and 1.7 &mgr;m ESA cross sections. The technique is applied to erbium‐doped, ion‐exchangeable silicate glasses yielding upconversion constants in the range of 1–10×10−18cm3/s. ©1995 American Institute of Physics.