Rules for Size and Speed of Pulleys

The driving pulley is called the Driver, and the driven pulley the Driven. If the number of teeth in gears used instead of diameter, in these calculations, number of teeth must be substituted wherever diameter occurs.

To find the diameter of the Driver; the diameter of the Driven and its revolutions, and also revolutions of Driver being given: Multiply the diameter of Driven by its revolutions, and divide the product by the revolutions of the Driver; the quotient will give the diameter of the Driver.
To find diameter of the Driven; the revolutions of the Driven, also diameter and revolutions of the Driver being given: Multiply the diameter of Driver by its revolutions, and divide the product by the revolutions of the Driven; the quotient will give the diameter of the Driven
To find the revolutions of Driver; the diameter and revolutions of the Driven, also diameter of the Driver being given: Multiply the diameter of Driven by its revolutions, and divide the product by the diameter of Driver; the quotient will give the revolutions of Driver.
To find revolutions of the Driven; the diameter and revolutions of the Driver, also diameter of the Driven being given: Multiply the diameter of Driver by its revolutions, and divide the product by the diameter of Driven; the quotient will give the revolutions of Driven.

Diam. of Driver = (D2 x S2) / S1

Diam. of Driven = (D1 x S1) / S2

Revs of Driver = (D2 x S2) / D1

Revs of Driven = (D1 x S1) / D2