To convert from reduced Snellen (RS) to metric (M) notation, one must divide the denominator by 50. In the above example 50/50 = 1M.
To convert from Reduced Snellen to Printer's point, divide the denominator by 6. To convert from Printer's point to metric, divide by 8. To convert from metric notation to reduced Snellen, multiply by 50; this will give you the denominator of the reduced Snellen equivalent.
A good rule of thumb is 1M = RS 20/50 = 8 point.
Below is the conversion triangle:
