Router speed and feed wizard
Answer four questions: your machine, the bit, the material and the cut. You get the spindle speed with every limit that set it named, the dial setting for your router, and on a CNC the chip load, feed rate and number of passes. One question at a time, or switch on Expert to see them all at once.
How the setup is worked out
The speed starts from the bit makers' published maximum for the bit's diameter, the same median the router bit speed calculator uses. A lower speed marked on your bit wins, because the bit's own mark is the limit for that bit. Then your machine: a router that tops out lower caps the speed, and one that can't run slow enough for a large bit is refused rather than rounded, because that bit should not go in that router.
If your router is saved with its speed dial, the wizard names the setting: the highest number on the dial at or below the speed, from the dial table in the maker's manual. The dial numbers are approximate, so treat it as a starting point.
On a CNC the feed is the speed times the flutes times the chip load, the median of the bit makers' chip load tables in the CNC feeds and speeds calculator. The cut is split into passes no deeper than the bit's diameter, the depth at which the makers give a full chip, and a machine with a slower top feed caps the feed, with the spindle speed that keeps the same chip. A router fed by hand gets no feed number: take several light passes.
Save your machines once in my shop. They stay on this device; a link you share carries the bit and the cut, never your machine.