  We present the observed correlations between rest-frame 8, 24, 70 and 160 um
monochromatic luminosities and measured total infrared luminosities L_IR of
galaxies detected by Spitzer. Our sample consists of 372 star-forming galaxies
with individual detections and flux measurements at 8, 24, 70 and 160 um. We
have spectroscopic redshifts for 93% of these sources, and accurate photometric
redshifts for the remainder. We also used a stacking analysis to measure the IR
fluxes of fainter sources at higher redshifts. We show that the monochromatic
mid and far-infrared luminosities are strongly correlated with the total
infrared luminosity and our stacking analysis confirms that these correlations
also hold at higher redshifts. We provide relations between monochromatic
luminosities and total infrared luminosities L_IR that should be reliable up to
z~2 (z~1.1) for ULIRGs (LIRGs). In particular, we can predict L_IR with
accuracies of 37% and 54% from the 8 and 24 um fluxes, while the best tracer is
the 70 um flux. Combining bands leads to slightly more accurate estimates. For
example, combining the 8 and 24 um luminosities predicts L_IR with an accuracy
of 34%. Our results are generally compatible with previous studies, and the
small changes are probably due to differences in the sample selection criteria.
We can rule out strong evolution in dust properties with redshift up to z~1.
Finally, we show that infrared and sub-millimeter observations are
complementary means of building complete samples of star-forming galaxies, with
the former being more sensitive for z<~2 and the latter at higher z>~2.
