The conversion factor
One pound equals exactly 0.453592 kilograms (rounded to 6 decimal places from the exact legal definition, 0.45359237). For a single pound, that factor is the direct answer: 1 lb = 0.453592 kg.
A worked example: 154.32 pounds
154.32 × 0.453592 = 69.998375 kg — very close to, but not exactly, 70 kg.
Why the result isn't exactly 70
The companion article on converting kilograms to pounds shows that 70 kg converts to 154.323584 lb, not the rounder 154.32 used here. Because 154.32 is itself already a rounded version of that more precise figure, converting it back doesn't quite recover the original 70 kg — it lands 0.001625 kg short.
What this means for round-tripping a conversion
Converting a value and then converting the result back only returns the exact original number when no rounding happened along the way. In practice, a weight already displayed to 2 decimal places has already lost some precision, so converting that displayed value back is converting an approximation, not the original exact figure.