How many?

Kilograms

The kilogram is a metric unit of measurement equal to 1,000 grams, and equivalent to approximately 2.205 lb).

Slugs

The slug is a derived unit of mass in a weight-based system of measures, most notably within the British Imperial measurement system and the United States customary measures system. A slug is defined as the mass that is accelerated by 1 ft/s2 when a net force of one pound (lbf) is exerted on it.