In the United States, Part 107 and Part 91 require pilots to stay 500 feet below clouds. Here is how you can calculate the bases so you do not get within 500ft.
Method 1
Find the temperate and dew point. If you look at this METAR for Miami International:
KMIA 221753Z 12006KT 10SM FEW017 BKN180 OVC250 29/24 A3004 RMK AO2 SLP171 60075 T02940244 10294 20244 58009
The temperature in Celsius is 29 and the dew point is 24 Celsius.
Method 2 (for Drone Pilots)
You can get one of those handheld sensors that shows the temperature and dew point. This is great for when you are not near an airport that has METARs. This also allows real-time updates while METARs can have a little lag.
Disclaimer Notice: The final number represents an approximation and should only be used as a guide. No guarantees or warranties are implied. This calculator is “as is” and you should use it at your own risk.
Aviation Attorney. FAA Certificated Commercial Pilot and Flight Instructor (CFI/CFII). Contributor at Forbes.com for Aerospace and Defense.