My answer is:
The taper is defined by the diameter of the workpiece throughout its length. The amount of taper defined by the ratio of the difference in the diameters of the taper to the length of the taper is known as the amount of taper. Examples of taper diameters are 1:4, or 0.5: 4 etc.

If you have any best answer, reply me

 

According to ASME Y14.5, if your taper follows a standard, specifying the taper name and number is probably best. Otherwise, there are 3 good ways, and 1 acceptable way:

1. As you indicated, a diameter at some point, plus a ratio of (diameter at one end to diameter at the other)/Length. Both would be basic.
2. A size tolerance combined with a profile of a surface tolerance
3. A composite profile tolerance.

The acceptable way is tolerance the diameter at both ends and the length across.

You'd probably have to see the standard to properly understand the first 3. I can help answer specific questions, but it's a bit lengthy to go into detail for each one