Form is defined as the rate of taper of a log or stem. Taper is the decrease in diameter of a stem of a tree or of a log from base upwards. The taper varies not only with species, age, site and crop density but also in the different parts of the same tree.

FORM FACTOR: Form factor is defined as the ratio of the volume of a tree or its part to the volume of a cylinder having the same length and cross-section as the tree. The form factors are of the following types:

a) Artificial Form Factor: This is also known as the breast height form factor. Here, the basal area is measured at breast height and the volume refers to whole tree both above and below the point of measurement.
b) Absolute Form Factor: For this form factor basal area is measured at any convenient height and the volume refers only to that part of the tree above the point of measurement.
c) Normal Form Factor: In this form factor basal area is measured at a constant proportion of the total height of the tree.

FORM QUOTIENT: It is the ratio of diameter to dbh. Form quotients are of two types:

a) Normal Form Quotient: It is the ratio of mid-diameter of a tree to its diameter at breast height.

b) Absolute Form Quotient: It is the ratio of a stem diameter at one half its height above the breast height to the diameter at breast height.

FORM HEIGHT: It is the product of form factor and the total height of the tree.

Form Height = Volume of tree/Basal area

FORM CLASS: It is one of the intervals in which the range of form quotient of trees is divided for classification and use.

FORM POINT RATIO: Form point is the point in the crown where wind pressure is estimated to be centered. Form point ratio is the relationship of height of the form point above ground level to the total height of the tree, usually expressed as percentage.