Diameter growth of an individual tree can be obtained by measuring the diameter at the beginning and end of a specified period and by taking the difference. Since annual increment is small, when instruments such as callipersand diameter tapes are used, measurements are commonly taken at intervals of several years. Repeated measurements of permanent plots may give precise result. Precise measurement of minute increments in diameter may be required in research.

1. In even aged plantation of one spp.
   • Early immature stage before canopy closure when rate of diameter growth is little affected by competition.
   • Responsive middle stage: On canopy closure ring width decreases but responds quickly to treatment such as thinning and fertilizing.
   • The final (mature stage) when ring width is narrow and is not so markedly responsive to treatment.
2. Diameter growth in natural forest
   • An early stage of extremely slow diameter (and height)growth while the sapling is dominated by overwood.
   • A middle stage when the tree is growing more rapidly but is still severely affected by its larger neighbors
   • The final stage when the tree is a dominant with a large, free, well developed crown and neighboring trees of same size are few and distant.

Whatever the structure of forest, rate of diameter growth depends on degree of competition. Though the width of ring of trees normally decreases as tree becomes older. The thinner wood layer added over a larger diameter or bole surface. So, the volume is greater than previous years. Age, rate of diameter growth depends upon soil moisture and amount of leaf functioning for photosynthesis process. Wider spacing among tree results in more root growing space and larger crowns which lead to faster dia growth.