What Is Golden Ratio?
The golden ratio (denoted φ, or phi) is approximately 1.618033988749... — an irrational number where, if a line is split into two parts, the ratio of the whole line to the longer part equals the ratio of the longer part to the shorter part. It shows up in geometry, art, and famously (though often overstated) in nature.
Example
If a line 1.618 units long is split into a piece of length 1 and a piece of length 0.618, the ratio of the whole (1.618) to the longer piece (1) equals the ratio of the longer piece (1) to the shorter piece (0.618) — both equal about 1.618.