SFM is the entry point for calculations. Recommended SFM is based on cutter material and stock material. Given a specific cutter material and stock, you can find recommended SFM values from the cutter manufacturer or from an online table.
RPM (Speed) = SFM x 12 / (π * Tool Diameter)
From this calculation, you can get your “speed.” This calculation determines the maximum speed for the tool and material. In other words, this is the “speed limit” rotating faster than this will cause your tool to age prematurely. You will often operate slower than this depending on your machine's spindle capabilities.
Approximation: RPM = 4 x SFM / Tool Diameter
When done with this calculation, pick a comfortable speed and use that to calculate the rest of your parameters.
Chip load is normally determined experimentally by the tool manufacturer. It is reported as IPT. You can use this number along with the RPM you calculated earlier to determine a feed rate.
If you can't find chip load anywhere, a conservative estimate is to divide the diameter of the cutter by 150.
A 1/4“ cutter with 2 flutes would yield the following result:
Chip Load = .25 / 150 = 0.00166”/tooth
Feed Rate = RPM x Chip Load x Number of Flutes
Using a speed of 5000rpm:
Feed Rate = 5000 x .00166 x 2 = 16.66 in/min
The rule of thumb is to cut no deeper than 1/2 of the diameter of the cutter if you're cutting a pocket using 100% of the tool.