Did not know about lightroom, but I see it's available in the crop tool in photoshop as well.It's available as an overlay in Lightroom...
Connected to the Fibonacci series, not to be confused with the Fabinocci sequence
Or if you are old school, sketch around a cigarette packet on the back of an envelope (ISTR that Marlboro packets are golden ratio)
That figures - I do almost all my batching and image editing in LR, so makes sense it's available in PSDid not know about lightroom, but I see it's available in the crop tool in photoshop as well.