The molar extinction coefficients, known also as molar absorptivity epsilon, of C-60 and C-70 fullerenes infrared absorption spectra were determined at room temperature on samples embedded in KBr pellets. Furthermore, the integrated molar absorptivity Psi of each absorption infrared band either of C-60 and of C-70 was measured and reported together with the relative intensity of the infrared absorption bands. These results can be useful in the quantitative determination of C-60 and C-70 fullerenes in space after the recent discovery that these molecules are present around the young planetary nebula Tc1.