How many?

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.

Stones

The stone or stone weight is an English and imperial unit of mass equal to 14 pounds (approximately 6.35 kg). The stone continues in customary use in the United Kingdom for body weight.