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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
D. L. ROCKWOOD AND L. G. ARVANITIS
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
John T. Woeste, Dean for Extension
FORESTRY GOES METRIC
D. L. Rockwood and L. G. Arvanitis
Assistant Professor and Professor, respectively,
School of Forest Resources and Conservation
The United States is gradually converting its standards of measure-
ment to the metric system. Speed limits, for example, will be given in
kilometers per hour effective July 1, 1978. By January 1, 1979, all
weather information and all distilled beverages will be expressed in metric
terms. Forestry, likewise, will employ metric weights and measures, and
the use of appropriate units must be anticipated and scheduled.
A number of agencies have been formed to assist the forestry profes-
sion in the transition to the metric system. A Committee on Metrication'
has been established by the Society of American Foresters to inform its
members on metrication and also to solicit input related to using the metric
system. Within the American National Metric Council, the Sector Committee
for Lumber and Wood Products coordinates activities in forestry and forest
products. A federal national metric board will be appointed by the Presi-
dent soon to handle public aspects of conversion. At this stage, most con-
version work is voluntary and takes place within the private sector of the
economy. Without a federal mandate, the changeover to the metric system
may take between 5 and 15 years.
Advantages of Conversion
Several benefits will be realized once the metric system is implemented.
The United States exchanges forest products with countries that solely use
the metric system for international trade. Thus, its export-import status
would be improved by metrication.
Metric units have relationships easy to remember since the units are
based on multiples of 10 (Tables 1 and 2). For example, the basic unit of
length, the meter, multiplied by 1000, becomes a kilometer. A 1/1000 of a
meter, on the other hand, is a millimeter. Appropriately dimensioned
units can be readily generated by use of the metric prefixes.
Basic units have definitions in terms of other base units that also
involve powers of 10. A liter equals 1000 cubic centimeters and, under
certain conditions, also has a mass of 1 kilogram. A hectare corresponds
to 10,000 square meters.
'Address: SAF Metrication Committee
U. S. Forest Service
P. 0. Box 3141
Portland, Oregon 97208
Table 1. Commonly used metric prefixes.
mega- x 106 (1 million)
kilo- x 103 (1 thousand)
hecta- x 102 (1 hundred)
deca- x 10' (1 ten)
deci- x 10-1 (1 tenth)
centi- x 10- (1 hundredth)
milli- x 10-3 (1 thousandth)
micro- x 10-6 (1 millionth)
Table 2. Definition of certain metric units.
ARE = 100 square meters LITER = 1000 cubic centimeters
= 1 cubic decimeter =
HECTARE = 10,000 square meters 1 kilogram
SQUARE KILOMETER = 100 hectares METRIC TON = 1,000 kilograms
STERE = 1 cubic meter
Our currency has many of these desirable features. One dime is 10 cents.
A dollar is 100 cents. A million dollars is 106 dollars or 108 cents. How-
ever, the rest of our current weights and measures, particularly in forestry,
is an overwhelming set of equivalences. A gallon equals 231 cubic inches.
An acre consists of 43,560 square feet. A mile equals 5,280 feet or 80
chains. A cord of wood has a stacked volume of 128 cubic feet. A yard
equals 36 inches. A ton is 2,000 pounds. And, the list goes on without
any ready comprehension to those not schooled in the system.
Another benefit that will accrue from metrication is the consolidation
of measurement units. The abundant terms expressing the yield of a tree---
cubic feet, cords, board feet by various log rules, all according to speci-
fied merchantability standards---are likely, for example, to give way to
simple metric expression of cubic volume or weight.
Metric Units in Forestry
Designation of metric units suitable for various forestry applications
(Table 3) is basically straightforward. However, the units chosen for each
measurement must be convenient, i.e., have a workable number of digits. A
tree diameter of 25 centimeters is awkward if expressed as 250 millimeters.
Also, the amount of pertinent information conveyed by the unit must be ap-
propriate, as shown by the description of stand basal area in square meters
per hectare. The U. S. basal area equivalent of one square meter per hectare
Table 3. Metric units and their forestry applications.
Diameter breast height of trees.
Tree stem diameters.
Diameter of logs and poles.
Width, thickness, and length of lumber
Plot area; basal area of trees.
Volumes of trees, logs, and wood products.
Mass of logs, trees, fertilizers, etc.
Mass of wood.
Basal area of forest stands.
Volume of forest stands.
Volume increment of forest stands.
Mass of forest stand.
is 4.356 square feet per acre, an amount that is quite acceptable as ade-
quately describing stocking of a forest stand. Consequently, providing
stand basal area in square meters per hectare without any decimal would be
adequate in practice.
Metric units in southern forestry generally provide sufficient informa-
tion without resulting in inconvenient numbers of significant digits (Table
4). Tree diameter and stand volume increment are given with the same number
of digits in metric as in U. S. units, while tree height and stand basal
area require fewer digits over the typical range of data. Tree volume,
trees per unit area, and stand volume require an additional digit to bracket
the usual forestry data.
Table 4. Representative correspondences between metric and U. S. units
in southern forestry.
Application Range of Values Application Range of Values
9.0-75.0 cm. 5.0-30.0 m.2/ha.
Tree Diameter 3.5-29.5 in. Stand Basal Area 21.8-130.7 ft.2/A.
5.0-35.0 m. 100-2,500 trees/ha.
Tree Height 16.4-114.8 ft. Stand Density 40.5-1011.7 trees/A.
.006-2.000 m.3 90.0-450.0 m.3/ha.
.21-70.63 ft.3 Stand 10.0-50.2 cds./A.
Stand Volume Increment 6-2.8 cds./A./yr.
Types of Conversion
Metrication in forestry will necessitate two types of conversions. One
type is classified as hard conversions, in which the physical dimensions
associated with a standard of measurement actually change. Soft conversions
do not entail physical changes but rather involve use of conversion factors.
Hard conversions will have more impact on forest products than on
forestry per se (Table 5). Foresters face acceptance of a new standard for
diameter at breast height (DBH), utilization of slightly altered merchant-
ability standards employed in forest inventory, and redefinition of the pro-
cedures for summarizing inventory data. Metric molules will create many
changes in forest products, as virtually every finished product will have
new dimensions. However, these new standards will not affect the expression
of yields from harvested but unprocessed wood. Yields from trees and stands
will most conveniently be expressed in cubic volume or weight.
Table 5. Examples of hard conversions in forestry.
A. Redefinition of breast height (currently 4.5 ft.)
Alternative 1 = 1.3 m. (4.29 ft.) used in most countries
Alternative 2 = 1.4 m. (4.57 ft.) used in New Zealand
B. Redefinition of tree merchantability standards
Top diameter = 9 cm. (3.54 in.)
Minimum merchantable height = 5 m. (16.4 ft.)
C. New diameter classes and class limits
10 cm. dbh class = 8.6 cm. to 11.5 cm. (3.39 in. to 4.53 in.)
D. New product dimensions
Plywood sheet = 12 dm. x 24 dm. (3.94 ft. x 7.87 ft.)
Doors = 200 cm. x 80 cm. (6.56 ft. x 2.62 ft.)
Soft conversions can be easily performed; existing measurements can be
changed to their metric equivalents by use of conversion factors as shown
by the following applications of Table 6:
25 in. x 2.54 cm. = 63.50 cm.
80 ch. x 20.1168 m. = 1609.3 m.
For converting metric units to U. S. units, the reciprocal terms are used:
40 cm. x .393701 in. = 15.7 in.
1000 m. x .0497097 ch. = 49.7 ch.
The number of soft conversions to be conducted in forestry includes
simple data, ranging from previously recorded tree heights to more compli-
cated inventory data such as stand and stock tables (Table 7). Instruments
such as hypsometers can be adapted by a mere change of scales, but previous-
ly calibrated equipment such as diameter tapes should be replaced by metric
Table 7. Examples of soft conversions in forestry.
A. Redefined lengths
Tree height = 28 m. (91.7 ft.)
Boundary line = 1400 m. (69.6 ch.)
B. New Areas
Property size = 40 ha. (98.8 acres)
C. Redefined weight
Tree size = 250 kg. (551 Ibs.)
D. Recalculated volume
Tree size = 1 m.3 (35.3 ft.3)
The most far-reaching soft conversion in forestry will be the transi-
tion of land measurements. All property must eventually be described in
metric units such as lengths and areas. Angles and bearings will likely
continue to be expressed in degrees. The transition will be gradual since
resurveys will be conducted only when property changes ownership.
Existing maps and aerial photos can be used by simply adding the appro-
priate metric scale. While such conversion does provide metric length and
area assessments, the derivation of the information is awkward since photo
distance and ground distance are not related by a power of 10.
Table 6. Metric-U. S. Equivalents
- in. m. ft.
.393701 .3048* 3.28084
ha. mi e2
metric ton ton
5 (oF 32)
9 OC + 32
metric ton/ha. ton/A.
- lb./ft.3 kg./ha. Ib./A.
.0624278 1.12085 .892180
*exact conversion factor
a/128 cubic feet per cord
Other common measurements can be changed to metric equivalents by
conversion factors. Known lengths in feet can be expressed in meters
when multiplied by .3048, and areas in acres are converted to hectares
when multiplied by .404686. Weight in kilograms is equivalent to weight
in pounds multiplied by .453592. Cubic foot volumes convert to cubic
meters by use of .0283168.
Certain existing relationships can generate metric output by use of
appropriate factors. For example, a tree volume equation of the form
ft.3 = bo + bi-D2-H
where D is DBH in inches and H is in feet.
can be made compatible with metric diameters and height by developing a
m3 = bo' + b1' D2 H
where bo' = .0283168-bo and
bi' = .01440-bi
More complex expressions, such as yield equations, may also be converted.
Computer data processing utilizing U. S. unit input and-output will require
reprogramming, but the effort will be manageable.
Implementing the Metric System
Metrication in forestry is best achieved by recognition of the compre-
hensive impact of the use of metric system and establishment of a suitable
schedule for making the transition. The conversion should begin immediately,
and its implementation proceed consistently.
Land measurements tract boundary lines and areas should be gradually
changed to metric units. As property ownership changes, resurveying and
associated recording can incorporate new terminology.
Existing maps and aerial photographs should have appropriate metric
scales applied as they are used. New maps and photos should be made with
suitable scales, a requirement that will necessitate institution of new
Forest inventory procedures will encompass a number of changes. Most
basic will be utilizations of new definitions of measurement and merchant-
ability. DBH measurement will be in accordance with the redefined breast
height. Stump heights and merchantable top diameters will change. Units
of merchantable length will also be revised.
The above changes in tree measurement will require field crews to
operate under new instructions. Tally forms must be revised to agree with
the new units. Some field equipment such as hypsometers with percentage
scales can continue in use, but metric field instruments, such as diameter
tapes, loggers tapes, and chains, would otherwise be more convenient and
Basic inventory techniques should also be revised. Sample plot sizes,
for example, should be in square meters for small plots and hectares for
larger plots. For variable plot sampling, metric prisms or relaskops would
Inventory summary methods will need changing. Metric basal area is
calculated as .00007854 times dbh in centimeters squared. Diameter classes
shown in summary tables will not only be different in magnitude but will
also reflect new standards of utilization. Log and tree yield expressions
will probably be limited to volume or mass units; numerous board foot ex-
pressions will likely be discarded. Therefore, revision of existing log
and tree volume equations will be required, and current computer programs
for inventory data processing must be modified. Stand yield equations
must also be brought in line with metric terminology.
Sufficient training of professional and technical staff will be required
to incorporate the metric system effectively into forestry. Forest product
manufacturers and consumers must become accustomed to new standards. Re-
searchers must develop new mensurational data for applications in forestry.
The advent of a better-defined and easier-used system of measurements
in forestry is approaching. While much present forestry data can be easily
converted to metric units, the most productive method of realizing the
advantages of the metric system is "to think metric" (Fig. 1). Conceptual-
ize the physical units in forestry in metric terms. In doing so, the transi-
tion away from the incongruous U. S. system of measurements will be expedit-
ed. As new metric information techniques are developed, forestry opera-
tions in the U. S. will not only be more sensible but will also be in tune
with forestry practices worldwide.
Bruce, D. 1974. Changing to the metric system. J. For. 72(12):
Bruce, D. 1976. Metrication: what's next? J. For. 74(11):737-8.
Grosenbaugh, L. R. 1973. Metrication and forest inventory. J. For.
Husch, B., C. I. Miller, and T. W. Beers. 1970. Forest Mensuration.
The Ronald Press, New York.
Myers, C. A. and C. B. Edminster. 1974. Conversion of tree-volume
equations to the metric system. USDA Forest Service Res. Note
Examples of metric concepts..
DBH = 25 cm.
Height = 20 m.
Gainesville to Tallahassee = 245 km.
Florida land area = 14 million ha.
Typical planting density = 1500 trees/ha.
Well-stocked forest stand = 20 sq. m./ha.
High forest stand growth rate = 20 cu.
UNIVERSITY OF^ FLORID
This publication was printed at a cost of $397.77, or
13.3 cents per copy, to identify the impact of the
metric system on forestry.
Single copies are free to residents of Florida and may be obtained
from the County Extension Office. Bulk rates are available upon
request. Please submit details of the request to C.M. Hinton, Publi-
cation Distribution Center, IFAS Building 664. University of
Florida, Gainesville, Florida 32611.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30,1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
K. R. Tefertiller, Director