Angle per side = arctan((D - d) / (2 x L)). A taper from 1.000 to 0.800 inch over 2 inches has a 2.862 degree angle per side (5.725 degree included) and 1.2 inches of taper per foot. Set the compound to the angle per side.
The compound is set to the angle per side, never the included angle. Tailstock offset only works for tapers between centers and is best kept to shallow tapers.
Tools for this job
The tooling this calculation is usually for, spread across the price range.
How does the taper calculator work?
Tapers are described three ways that mean the same thing: diameters over a length, taper per foot, and angle. Lathe compounds are graduated in degrees per side, so the angle per side is the number to set. Check the result with bluing on a mating part or with a dial indicator along the length.
Frequently asked questions
Should I set the compound to the included angle?
No. The compound swivels the tool path relative to the spindle axis, so it must be set to half the included angle, the angle per side. Setting the included angle doubles the taper, which is the single most common taper mistake.
Keep going
Formulas are standard shop math; starting speeds are conservative conventions for hobby machines. Not professional engineering advice. Wear eye protection and keep hands, gloves and sleeves clear of rotating work.