Find the speed a machine will run at, or the pulley you need to hit a target RPM. Includes belt slip and electric motor speed at any supply or VSD frequency.
Driven RPM = driver RPM × driver pulley diameter ÷ driven pulley diameter, less about 1–2 % for V-belt slip. Timing belts have no slip.
On 50 Hz a 4-pole motor's synchronous speed is 1 500 rpm; at full load it typically runs at about 1 440–1 480 rpm. Use the nameplate speed when you have it.