The pound (lb) is the main unit of weight in the US customary system. It is divided into 16 ounces. NIST's conversion factors list the avoirdupois pound as 0.4535924 kg.
Conversion
kg = lb × 0.4535924
lb = kg ÷ 0.4535924 (about kg × 2.2046)
oz = lb × 16
Example
A 5 lb bag holds 5 × 16 = 80 oz, which is 5 × 453.59 = 2,268 g or 2.268 kg. To find pounds from kilograms, 70 kg ÷ 0.4535924 = 154.3 lb.
The ounces in a pound guide has the chart and worked examples; how many grams in an ounce covers the metric side. The converters kg to lbs, lbs to oz and pounds to grams handle other values.
Pound of weight vs pound of money
The British pound sterling is a currency and unrelated to the unit of weight, even though the names share a root.