DBH = Diameter at Breast Height
= 2 r
where,
r is radius of stem

Girth = Perimeter of Stem at Breast Height
= 2 πr

Thus,

Gbh = Dbh * π

Under Bark vs Over Bark

DBH

DUB = DOB –2 t

Girth

g = g’ –2 π t

where g = g.u.b., g’ = g.o.b., t = bark thickness

Ratio of UB and OB

Once DBHUB has been calculated it can be inserted into a ratio and used to reduce the over bark volume to an approximate under bark volume. The ratio is:

Ratio = (DBHUB)²/(DBHOB)²