Speeds and feeds are the most important factors to consider for best results from cutting tools.  Improper speeds and feeds often cause low production, poor quality, and damage to the tool.  Too high a speed or too light a feed leads to rapid wear and dulling of the cutter, reducing tool life.
Speed is measured in peripheral feet per minute.  It is often referred to as cutting speed or surface speed.  Feed is normally measured and stated in inches per minute (IPM).  It takes into consideration the number of cutting teeth (or flutes), the feed per tooth (or cutting edges), and the revolutions per minute.  Feed recommendation tables for drills generally are based upon two flute drills.
In establishing operating conditions, all feeds rates should be calculated from the chip load or feed per tooth.  The highest possible feed per tooth will usually give longer tool life.  However, excessive feeds may overload the tool causing chipping of the cutting edges or breakage.
Following are many of the commonly used formulas for calculating operating parameters for cutting tools:
SFM: Surface Feet per Minute/Cutting Speed:  .262 X RPM X D (D=Diameter)
RPM: Revolutions Per Minute/Rotational Speed: (3.82 X SFM)/D or SFM/(.262 X D)
IPM: Inches Per Minute: Machine Feed Rate: RPM X IPR or T X IPT X RPM (T= # of teeth)
IPT: Inches Per Tooth/Feed Per Tooth: IPM/(RPM X T)
IPR: Inches Per Revolution-Feed Per Revolution: IPT X T or IPM/RPM
Inches to mm: Inches X 25.4 or Inches/ 0.03937
MM to inches: mm/25.4 or mm X 0.03937
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Thanks (and a gift to) Dick Ruetz for suggesting this topic.

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