Tommy,
I'm sure someone here will have a nice formula for working it out given the prevailing temperature, dewpoint and how many days it is since they last changed their underwear.
But personally, I prefer to read the cloud tops from MetForm 215 - it's far easier! (And it saves having to worry about when I changed my underwear, too!)
Also, it's not uncommon, if the lowest cloud layer is only scattered and not very deep, to be able to see roughly where the tops are from below, looking between the gaps - maybe not with any real accuracy, be enough to decide whether it's realistic to try to get on top, at least.
FFF
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