**Pulley Calculator. RPM, Belt Length, Speed, Animated Diagrams**
https://www.blocklayer.com/pulley-belteng.aspx

Enter any 3 known values to calculate the 4th If you know any 3 values (Pulley sizes or RPM) and need to calculate the 4th, enter the 3 known values and hit Calculate to find the missing value. For example, if your small pulley is 80mm diameter, and spins at 1000 RPM, and you need to find the second pulley size to spin it at 400 RPM, Enter Pulley1 80, Pulley 1 RPM 1000, Pulley 2 RPM 400, and ...

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