Many astrophysical fluids are strongly magnetized and in turbulent state. Since magnetic fields affect many physical processes, measuring their strengths is of great importance. First, I will talk about a technique called Davis-Chandrasekhar-Fermi (DCF) method, which is the most popular method for obtaining magnetic field strengths in molecular clouds. The DCF method is based on polarized emission from dust grains. Interstellar dust grains tend to be aligned with magnetic field and thermal emission from aligned grains is polarized in the direction perpendicular to magnetic field. Therefore, if we observe polarization of thermal radiation from dust grains, we can derive information about magnetic field. Second, I will discuss the limitations of the DCF method. Third, I will talk about a modified DCF method. Fourth, I'll talk about a technique that can remove a large-scale (e.g., hourglass-shaped) magnetic field component, which make it difficult to correctly measure the strength of magnetic field in the cloud.