# Converting magnitude to dBs

I have seen people using 10*log10 and/or 20*log10 while converting magnitude to dBs. What are the differences and which one is valid?

• $10 \cdot \log_{10}$ is for power ratios
• $20 \cdot \log_{10}$ is for voltage/pressure/etc ratios (these are called "field quantities" or "root-power quantities")