Temperature is an important physical parameter in astrophysics and we show that it can be determined in hot thin plasmas with only 1-10 percent energy resolution soft X spectra. The soft X-ray region from 40 to 10 keV has many lines for plasmas with cosmic abundance. These lines are sensitive to the temperature of the source. We analyze over 2000 lines in the 40 to 10 keV range. Surprisingly, many line blends remain that can be used for a useful temperature determination. For example, for an energy resolution of 5 percent, 23 line features are expected to be observed for an optically thin plasma of temperature 0.05 keV/k(B), many lines contribute to each feature. The feature in the energy interval E=0.0425-0.0467 keV consists of 34 lines. We show that these line features can be used to determine the source temperature.